Bruttus, maybe the following example will make it a little more obvious for you, that you will never be able to take all of our fiefs from us:
Back when UIF and the Coalition were active on EU, Hetman (Undoubtedly one of the best commanders Strat has ever seen) lead battles against villages that were much harder to attack than Ibiran.
It always played like a field battle, nowhere near a siege.
I cannot recall a single village attack that the UIF did not win.
Yet when attacking castles, even those much easier than Jelbegi Castle, it took thousands, some castles even tens of thousands of troops to capture.
Now you are undoubtedly not so bright when it comes to commanding.
You did not even win the Ibiran attack against an opponent with inferior gear. (And do not even start about being outmerced. A difference of 3 mercs does not qualify being called 'outmercing')
Jelbegi Castle is, as Heskey already stated, an incredibly difficult castle to attack.
So let us do some maths, I know you are pretty shit at maths, since we are the bigger faction and all, so let me take you by the hand on this one:
Let us assume you need 2 troops to kill 1 of us in a siege.
2k troops garrison = 4k troops attacking force.
Those 4k troops obviously need to be fully equipped. Sounds expensive.
Given the fact, that building a siege tower is basically impossible on that castle, you need ladders.
Those are not nearly efficient at keeping up a constant stream of attackers.
So we assume you lose 250 troops due to running out of time per battle.
You attack with 1k armies each, so 1k troops wasted right there.
So you need another 1k army to make up for that loss.
That makes a total of 5k fully geared troops.
Now those 2k troops are obviously not the only ones we have. So in case we decide to reinforce the castle, putting another 1k troops in there, you will need another 2,5k troops.
That makes about 7.5k troops. Now you might get lucky and all, so let us say you will not need one of those armies, still 6.5k fully equipped troops.
Now this requires all armies to be ready to attack right after one another. So you need at least 6 fully active members that will be able to pull this off.
Attacking with 2k armies will make you lose even more troops due to time, so I will not go through that one.
Also breaking a wall will make your troops end up in the courtyard. There they will get shot and still have to ladder up on the walls. So like shooting fish in a barrel, so will not go through those maths either.
All in all, if you talk about whiping us off the map, I envy you for having so much gold, and so many troops. While at the same time I despite you for not putting all those troops and gear you have to good use while probably wanking off to them in your fiefs.
Short note: If you do go for this, we will just intercept one or two armies to delay the siege, or we will take your fiefs in the meatime while your troops are out hitting the Jelbegi Castle walls with their swords. While this works in Age of Empires, you might have a hard time setting them on fire in cRPG.