adding units it is not just adding them to EDu.
1-add them to edu
2-add them to DMB (use alex it has more capacity which I added for) and change their root like :
Spoiler Alert, click show to read: 
type legio_i_italica ;use for legio_i_italica (Also given to Senate)
skeleton fs_pilum, fs_gladius
indiv_range 40
texture seleucid, eb/data/models_unit/textures/imperial/legio_i_italica.tga
model_flexi_m eb/data/models_unit/Legionary_ii_high.cas, 15
model_flexi_m eb/data/models_unit/Legionary_ii_med.cas, 30
model_flexi_m eb/data/models_unit/Legionary_ii_low.cas, 40
model_flexi eb/data/models_unit/Legionary_ii_lowest.cas, max
model_sprite seleucid, 60.0, eb/data/sprites/rs/romans_brutii_legio_i_italica_sprite.spr
model_tri 400, 0.5f, 0.5f, 0.5f

3-copy whole files written there in models unit folder
4-add units info and battle tga images

if you omit one of the these process you will have a certain CTD!

also if you want to play with them in not just in custom battle (the processes explained above just add units for custom battle!) also for campaign map :
-open EDB
find the faction MIC and put codes like:
Spoiler Alert, click show to read: 
recruit "legio ii augusta" 0 requires factions { seleucid, } and hidden_resource SW and hidden_resource B and hidden_resource y1 and hidden_resource n2 and hidden_resource n4 and hidden_resource y8
recruit "legio iii gallica" 0 requires factions { seleucid, } and hidden_resource SW and hidden_resource B and hidden_resource y1 and hidden_resource y2 and hidden_resource n4 and hidden_resource n8
recruit "legio iii gallica" 0 requires factions { seleucid, } and hidden_resource EA and hidden_resource C and hidden_resource y1 and hidden_resource n2 and hidden_resource n4 and hidden_resource y8
recruit "legio iii augusta" 0 requires factions { seleucid, } and hidden_resource SW and hidden_resource B and hidden_resource y1 and hidden_resource n2 and hidden_resource y4 and hidden_resource n8
recruit "legiov alaudae" 0 requires factions { seleucid, } and hidden_resource SW and hidden_resource B and hidden_resource y1 and hidden_resource n2 and hidden_resource n4 and hidden_resource y8
recruit "legiov alaudae" 0 requires factions { seleucid, } and hidden_resource NW and hidden_resource A and hidden_resource y1 and hidden_resource n2 and hidden_resource y4 and hidden_resource y8
recruit "legio vi ferrata" 0 requires factions { seleucid, } and hidden_resource SW and hidden_resource B and hidden_resource n1 and hidden_resource n2 and hidden_resource n4 and hidden_resource y8
recruit "legio vii cpfidelis" 0 requires factions { seleucid, } and hidden_resource SW and hidden_resource B and hidden_resource n1 and hidden_resource y2 and hidden_resource n4 and hidden_resource y8
recruit "legio vii cpfidelis" 0 requires factions { seleucid, } and hidden_resource NW and hidden_resource B and hidden_resource n1 and hidden_resource n2 and hidden_resource n4 and hidden_resource n8
recruit "legio viii augusta" 0 requires factions { seleucid, } and hidden_resource SW and hidden_resource B and hidden_resource n1 and hidden_resource y2 and hidden_resource y4 and hidden_resource n8
recruit "legio viii augusta" 0 requires factions { seleucid, } and hidden_resource NW and hidden_resource C and hidden_resource y1 and hidden_resource y2 and hidden_resource n4 and hidden_resource n8
recruit "legio ix hispana" 0 requires factions { seleucid, } and hidden_resource NW and hidden_resource A and hidden_resource n1 and hidden_resource n2 and hidden_resource y4 and hidden_resource y8


If you do not know the private hidden sources of certain province open descr_regions in campaign map base folder you could find their hidden resource codes at the end of their descriptions that I draw with red and add them EDB as I have added the lines above (they are green above):

Spoiler Alert, click show to read: 
Adiabene
Arbela
romans_scipii
Kardouchoi
194 218 61
copper, river, persia, pahlavahome, EA, C, n1, n2, y4, n8
5
1


Adurbadegan
Phraaspa
romans_scipii
Alarodoi
61 239 246
tin, copper, textiles, mixed, variantea, pahlavahome, EA, C, n1, y2, n4, n8
5
1


Aemilia
legion: Aemilia
Bononia
gauls
Boii_Galla
164 142 123
SW, B, n1, n2, y4, n8
5
2


and thank God if you have successfully manage to add them and EB will open without error messages or CTDs.

P.S. If you want to use this models for yourself you can use privately but you have to ask for permission from the dev team who made them if you want to publish them as a submod.
I have added RS Legions on my EB so I can use them but I cannot publish them, sorry

I hope it helped.

Atra