I've tried outlasting them but it seems endless. I then tried to just kill them all at once via imp alacrity/timestop via wish and mass aoe dmg spells after removing mage protections via remove/dispell magic but they still spawn in. My question is will this fight be over after x amount of time and its just a matter of survival, or is there something else?

i just waited it out via malaison + emotion/slow/hold spells with wish for refresh while melee tanked with hardiness + regen

Nice tactics, risky and brave, that I used once (second runthrough) and it worked like a charm: protect your fighters against melee damage (100%), level drain and domination spells. Ignore, yes, ignore summons and just attack him immediately on enter with improved hasted fighters but don't activate your offensive hla's yet. Wait until your hits actually connects the target and then activate critical strike hla (this is what makes this tactic so mean ;]) killing him on the spot. Ah, one more thing - watch for master vampires! These abominations are extremly dangerous if left alone for too long.

The cheesy method of hastily moving characters to Orcus before the cutscene kicks in, and killing Orcus without fighting his minions (the grandlords) is already blocked in IA v6. Now, in v6, it doesn't even matter if you move to Orcus before the grandlords appear, because he can't be killed before them. As long as you are playing v5, try to win the battle in the intended way and wait for the grandlords and kill them before Orcus. In v6, it's all fixed and the cheesy method won't work anyway.

I rush in with 2 warriors to get the focus of orcus and the grandlords.
Then I reposition my other 4 characters and use them to get rid of the other summons.
Gradually my warriors will kill one grandlord and proceed to the next, which is repeated until all are gone. Potions of barbarian essence get used here to keep the warriors alive, but in general they are not enough to keep the warriors alive for the entire fight. I have to use high AC, hardiness, armor of faith and also the "Regeneration" spell (which goes faster with improved haste) to keep them alive. Sometimes I also use a properly protected mage as a distraction, but that goes through the protection scrolls rather quickly and if you time it wrongly and have no stoneskin on, you can say goodbye to the mage.

I wound up having the tanks + anomen killing the GLord that spawns next to anomen. Then i moved him in the back with the casters while the 3 tanks took out the remaining summons. I had priority on vampire masters/brides-->GLords-->Lords. Once i had a clear avenue through, i moved the 3 casters to the bottom for resto/wish. Orcus wasnt that bad once they were dead. I wound up using 6 barb essences on the 3 tanks (2 left i believe) and the fight wasnt too bad with 80% (95% for Valygar via FoDW) damage reduction from barb essences + wish hardiness.

Doh. False assumption. I mean AFTER the cutscene. Massive attack on Orcus AFTER, not before the cutscene. Watch carefully for your mages protections, watch for your cleric protections very carefully (keep the grandlors away from him), kill Orcus first and then all his minions. It depends on my decision, as a player, who I will attack first, right? Or maybe it's a modder decision who I should attack first? ;]

Of course, it's your choice whom you want to attck first; but attacking Orcus before killing all of the grandlords is a waste of time, because he won't fall (is not intended to fall) as long as his grandlords are around. The battle has never been intended to be won in that way even in previous versions of the mod. It was possible to win the battle in that unintended way in v5, but as I said, it was an exploit which is already blocked and fixed in v6.

The only opponents can see through invisibility are the orc mages, so you just need keep killing the mages until there is none, then let all party members drink invisibility potions and wait for the end.