Hey Pilo T, the castle breaking of which you speak can actually be fixed using the editor
View the Mission Templates section in the editor.
Go to mst_castle_attack_walls
Then to spawn records tab at the top
On the left theres 5 entrys: 0,0,10,11,12
Click on 10 and tick the box 'enemy party'
Do the same for 11 and 12 and its all fixed
And as for the people who cant defend castles...get a party to follow you...enter your castle...then click the rest button. The enemy party will sit over your castle and when your done resting they'll attack it.