There's a few posts on this but none of them explain it so I will.

MAKE A BACK UP COPY OF THE DESCR_STRAT JUST INCASE YOU MESS UP THEN YOU CAN REPLACE IT.

First you have to make the senate, brutii and scipii unplayable which is easy so copy this:

Code:
campaign		imperial_campaign
playable
	romans_julii
	egypt
	seleucid
	carthage
	parthia
	gauls
	germans
	greek_cities
	macedon
	pontus
	armenia
	dacia
	scythia
	spain
	thrace
	numidia
	britons
end 
unlockable

end
nonplayable
	romans_brutii
	romans_scipii
	romans_senate
	slave
end
Then scroll down to the start of the julii's bit of text and look for a line that is in between this:
Code:
faction	romans_julii, comfortable caesar
denari	5000
settlement
and says super_faction senate. Delete that line so it looks like the code posted above. Under that there is the settlemens that the julii own, Arretium and Ariminum leave those alone keep scrolling down and you will get to the armies garrisoned inside the settlements, the diplomats and spys traits and skills same for the naval boats.

Then under those it's the family mebers part. Leave that aswell as you don't want your faction dieing half way through the game that looks like:
Code:
character_record		Amulius Julius, 	male, command 0, influence 0, management 0, subterfuge 0, age 13, alive, never_a_leader
character_record		Manius Julius, 	male, command 0, influence 0, management 0, subterfuge 0, age 10, alive, never_a_leader
character_record		Decius Julius, 	male, command 0, influence 0, management 0, subterfuge 0, age 7, alive, never_a_leader
character_record		Marcus Julius, 	male, command 0, influence 0, management 0, subterfuge 0, age 3, alive, never_a_leader
character_record		Faustina, 	female, command 0, influence 0, management 0, subterfuge 0, age 48, alive, never_a_leader
character_record		Poppaea, 	female, command 0, influence 0, management 0, subterfuge 0, age 29, alive, never_a_leader
character_record		Alypia, 	female, command 0, influence 0, management 0, subterfuge 0, age 29, alive, never_a_leader
character_record		Claudia, 	female, command 0, influence 0, management 0, subterfuge 0, age 28, alive, never_a_leader
character_record		Fadia, 	female, command 0, influence 0, management 0, subterfuge 0, age 13, alive, never_a_leader

relative 	Flavius Julius, 	Faustina,		Lucius Julius,	Quintus Julius,	Vibius Julius,	end
relative 	Lucius Julius, 	Poppaea,		Fadia,	Decius Julius,	Marcus Julius,	end
relative 	Quintus Julius, 	Alypia,		Amulius Julius,	end
relative 	Vibius Julius, 	Claudia,		Manius Julius,	end
under that you will get
Code:
faction	romans_brutii, balanced stalin
denari	5000
With the super_faction senate or something similar, delete that line again.
Under that bit of text is the text for the settlements that the brutii have highlight all that and cut it. Scroll up til you get to thi bit of text inside the julii's faction detials:
Code:
	building
	{
		type hinterland_farms farms
	}
}
then get two new lines after the last curly bracket in the code posted above and press control and V or right click and paste so now it should look like ths for the julii:
Code:
faction	romans_julii, comfortable caesar
denari	5000
settlement
{
	level large_town
	region Etruria

	year_founded 0
	population 4000
	settlement_tax 51
	plan_set default_set
	faction_creator romans_julii
	building
	{
		type barracks militia_barracks
	}
	building
	{
		type core_building governors_villa
	}
	building
	{
		type port_buildings port
	}
	building
	{
		type defenses wooden_pallisade
	}
	building
	{
		type hinterland_farms farms
	}
	building
	{
		type hinterland_roads roads
	}
}

settlement
{
	level large_town
	region Umbria

	year_founded 0
	population 3500
	settlement_tax 51
	plan_set default_set
	faction_creator romans_julii
	building
	{
		type barracks muster_field
	}
	building
	{
		type core_building governors_villa
	}
	building
	{
		type defenses wooden_pallisade
	}
	building
	{
		type hinterland_roads roads
	}
	building
	{
		type hinterland_farms farms
	}
}

settlement
{
	level large_town
	region Apulia

	year_founded 0
	population 4500
	settlement_tax 51
	plan_set default_set
	faction_creator romans_julii
	building
	{
		type core_building governors_villa
	}
	building
	{
		type equestrian stables
	}
	building
	{
		type barracks muster_field
	}
	building
	{
		type port_buildings port
	}
	building
	{
		type defenses wooden_pallisade
	}
	building
	{
		type hinterland_roads roads
	}
	building
	{
		type hinterland_farms farms
	}
}

settlement
{
	level large_town
	region Bruttium

	year_founded 0
	population 4300
	settlement_tax 51
	plan_set default_set
	faction_creator romans_julii
	building
	{
		type barracks muster_field
	}
	building
	{
		type core_building governors_villa
	}
	building
	{
		type defenses wooden_pallisade
	}
	building
	{
		type hinterland_roads roads
	}
	building
	{
		type hinterland_farms farms
	}
}
Now you need to define the units to go inside those settlements you gave to the julii.

So hightlight and cut this:
Code:
character	Tiberius Brutus, named character, leader, command 0, influence 0, management 0, subterfuge 0, age 52, , x 114, y 57 
traits GoodCommander 1, NaturalMilitarySkill 1, GoodAttacker 1, PoliticsSkill 2, Intelligent 1
ancillaries drillmaster
army
unit		roman generals guard cavalry early				exp 1 armour 0 weapon_lvl 0
unit		roman hastati				exp 1 armour 0 weapon_lvl 0
unit		roman velite				exp 1 armour 0 weapon_lvl 0

character	Aulus Brutus, named character, heir, command 0, influence 0, management 0, subterfuge 0, age 34, , x 111, y 68 
traits GoodCommander 1, PoliticsSkill 2, Rabblerouser 2, GoodAdministrator 2
ancillaries quartermaster
army
unit		roman generals guard cavalry early				exp 1 armour 0 weapon_lvl 0
unit		roman hastati				exp 1 armour 0 weapon_lvl 0
unit		roman velite				exp 0 armour 0 weapon_lvl 0

character	Marcus Attius, admiral, command 0, influence 0, management 0, subterfuge 0, age 29, , x 120, y 64 
army
unit		naval biremes				exp 0 armour 0 weapon_lvl 0
unit		naval biremes				exp 0 armour 0 weapon_lvl 0
unit		naval biremes				exp 0 armour 0 weapon_lvl 0

character	Luca Antonius, spy, command 0, influence 0, management 0, subterfuge 0, age 23, , x 116, y 62 
traits GoodSpy 4

character	Caius Flaminius, diplomat, command 0, influence 0, management 0, subterfuge 0, age 23, , x 112, y 63 
traits GoodDiplomat 3

character	Amulius Brutus, named character, command 0, influence 0, management 0, subterfuge 0, age 31, , x 116, y 64 
traits GoodCommander 1, NaturalMilitarySkill 2, PoliticsSkill 1, Intelligent 2
ancillaries doctor
army
unit		roman generals guard cavalry early				exp 0 armour 0 weapon_lvl 0
unit		roman light cavalry				exp 1 armour 0 weapon_lvl 0
unit		roman hastati				exp 0 armour 0 weapon_lvl 0
unit		roman hastati				exp 0 armour 0 weapon_lvl 0
unit		roman velite				exp 0 armour 0 weapon_lvl 0

character	Vibius Brutus, named character, command 0, influence 0, management 0, subterfuge 0, age 30, , x 114, y 63 
traits GoodCommander 1, GoodAdministrator 2, PoliticsSkill 1, Intelligent 2, MathematicsSkill 2
army
unit		roman generals guard cavalry early				exp 1 armour 0 weapon_lvl 0
unit		roman hastati				exp 0 armour 0 weapon_lvl 0
unit		roman velite				exp 0 armour 0 weapon_lvl 0
Then go to where there is similar code for the julii and after the last line of text for
Code:
unit		roman velite				exp 1 armour 0 weapon_lvl 0
hit enter twice and paste it in there.

now what you should have left for the brutii is the following:
Code:
faction	romans_brutii, balanced stalin
denari	5000

character_record		Cassius Brutus, 	male, command 0, influence 0, management 0, subterfuge 0, age 14, alive, never_a_leader
character_record		Titus Brutus, 	male, command 0, influence 0, management 0, subterfuge 0, age 10, alive, never_a_leader
character_record		Cornelius Brutus, 	male, command 0, influence 0, management 0, subterfuge 0, age 7, alive, never_a_leader
character_record		Oppius Brutus, 	male, command 0, influence 0, management 0, subterfuge 0, age 3, alive, never_a_leader
character_record		Galla, 	female, command 0, influence 0, management 0, subterfuge 0, age 50, alive, never_a_leader
character_record		Hostia, 	female, command 0, influence 0, management 0, subterfuge 0, age 30, alive, never_a_leader
character_record		Lucilla, 	female, command 0, influence 0, management 0, subterfuge 0, age 28, alive, never_a_leader
character_record		Paulina, 	female, command 0, influence 0, management 0, subterfuge 0, age 12, alive, never_a_leader

relative 	Tiberius Brutus, 	Galla,		Aulus Brutus,	Amulius Brutus,	Vibius Brutus,	end
relative 	Aulus Brutus, 	Hostia,		Paulina,	Titus Brutus,	Oppius Brutus,	end
relative 	Amulius Brutus, 	Lucilla,		Cassius Brutus,	Cornelius Brutus,	end
Delete all of the family member stuff so your just left with
Code:
faction	romans_brutii, balanced stalin
denari	5000
and thats the settlements that the brutii have under your control as the julii.

What you do now is replace the traits and ancillaries and make him into a normal general, I think this is your choice to do this but I do it anyway just to make sure.

I will use Tiberius Brutus for this as he's the first family member for the brutii. The code below is whats there for him and under that are his men.
Code:
character	Tiberius Brutus, named character, leader, command 0, influence 0, management 0, subterfuge 0, age 52, , x 114, y 57 
traits GoodCommander 1, NaturalMilitarySkill 1, GoodAttacker 1, PoliticsSkill 2, Intelligent 1
ancillaries drillmaster
army
unit		roman generals guard cavalry early				exp 1 armour 0 weapon_lvl 0
unit		roman hastati				exp 1 armour 0 weapon_lvl 0
unit		roman velite				exp 1 armour 0 weapon_lvl 0
The bit you need to replace is
Code:
named character, leader, command 0, influence 0, management 0, subterfuge 0,
And just replace that with
Code:
general,
You must leave
Code:
age 52, , x 114, y 57
As thats his age and where he starts the game.

Then you need to delete his traits and ancillaries
which are
Code:
traits GoodCommander 1, NaturalMilitarySkill 1, GoodAttacker 1, PoliticsSkill 2, Intelligent 1
ancillaries drillmaster
And be left with
Code:
character	Tiberius Brutus, general, age 52, , x 114, y 57 
army
unit		roman generals guard cavalry early				exp 1 armour 0 weapon_lvl 0
unit		roman hastati				exp 1 armour 0 weapon_lvl 0
unit		roman velite				exp 1 armour 0 weapon_lvl 0
Do that for the rest of the settlements and generals for the scipii and the senate then save and quit. run your game and it should work fine if you have done it properly then when the game opens the senate missions will no longer be there, you will however get 3 messages saying that the senate, brutii and scipii have been destroyed. DO NOT CLICK THE SENATE TAB OR SENATE OFFICES BUTTON AS YOU WILL GET A CTD.