This is a "Tranquil Getaway" progressed game. It took me some time to get it done, but finally!
I defeated Emir Omar, an archer army is essential here, leave them on strategic spots to block Abbot attacks. I left 3 big archer packs on Emir's island, the one on the very left is the one to defend enemy attacks, no one passes with this, the one under that is supposed to be your next army to attack, of course, you will build your own melee army to enter. Use this archer army wisely, the reason it has shields is to protect archers, it is super-effective, more shields wouldn't spare on it. Use the number selection thing to control shields and archers & crossbows as different things but keep them together always!
The other mounted archers are there to defend trebuchets from flanks; These trebuchets are also essential to destroy Abbot's ballistas, they have an enormous range and are annoying as hell, they are the reason I put the archers to the west too much. The shields work amazingly here as well, I settled a pack of engineers to build more shields if they are destroyed. The tower from the back with mangonel can reach your trebuchets so also attack it. A big solution for them not to build towers again is to leave them mid-destroyed, just like the one on the right-down corner of the castle. Leaven 'em like that if you can, also, destroy their granaries & buildings this way, you get a free range to do it.
I left other trebs' under the active ones if you happen to destroy the one I manage to leave unrepairable, so mind not to do it, it is hard to reach that point. Once you have the yellow one, it is just time to re-build your army and charge, they defend more than attack, so watch out!
Good luck, hope it helps fellers!
NOTE: If you disband anyone, food will start disappearing! Recruit them or make them work!