You need to use spies in your own towns to combat the unrest. If unrest is high it is usually due to enemy spies infiltrating your towns. Otherwise you didn't really give much info on how many troops you have garrisoned, your tax levels, or if religion is hurting you. Perhaps you could give some more explanation and detail and we could assist you more.

If the mongols are invading Italy they must have dominated the eastern portion of the map in which case they will prove a handful. Try to fight them in forests or hilly terrain where you can get in cover where their arrows and cavalry will be handicapped.

I've beaten 2 h/vh campaigns and I still don't think I'm all that great, so I'm sure with some help and nudges in the right direction you'll get the hang of it.