couple of questions.

1. is udk in stoneskin?
2. can you post all of your undead champs?
3. how much time/effort can you spare for this? worst case scenario, you can always manual the boss fight and bail out before the end if gorgorab can't get his revive timed properly.

That boss ignores defense.

Also has a stun that can't be resisted, but it can be blocked. Do you have mausoleoum mage?

Poisons and burns won't boost it's tm.

I have Mausoleoum Mage.  

I have 3 years invested in this so far to get Lydia.  I will do what has to be done.  

UDK is not in Stoneskin.  My Stoneskin gear is not that great.  

it might be worth doing anyway. udk really just needs to tank as many hits as possible and a stoneskin buff will most likely improve his ability to do that. you probably would only need 4 pieces since if you build him without speed the boss will get several turns before his first one and destroy the buff.

for an overall team, i'm thinking gorgorab, udk, rotos, maybe graal for his aura, but im not seeing a great fifth option from the ones you listed here.

MM for block debuffs