Okay based on the information:
-We don't want to hit Under-Karagril, Karak Drazh is attacking it HARD, better to let the Skaven soak the casualties than for us to.
-We want to hit Kvynn-Wyr. Its uncontested, we just need to move siege engines in with a garrison force. This is basically the only way we're going to pull it off without Irondrakes and a Slayer Throng.
-We want to hit Clan Mors within the next 2 hours, but we want to hit as hard as possible in that instant.
...actually, does anyone think cleaving Clan Mors into two unconnected portions might be to our benefit?
They're committed FULLY into Eshin and Karagril. And in Karagril only in one direction. That means the Caldera is basically empty because nobody but dwarves can attack it and obviously dwarves wouldn't do it.
Take the wide open Caldera, fortify the perimeter while Mors is too stuck in to Yar and Karagril to do anything about it.
Thinking the Caldera is empty seems folly.
The entire Skaven paradigm is "we have reserves", so I would be rather surprised if Mors didn't have troops in reserve in the Caldera to respond to either Under-Karagril getting overwhelmed or an assault on the Under-Citadel. Mors isn't stupid, desperate, yes, but not stupid. We already know they work on an elastic defense system, Mors wouldn't attack Eshin without at least some troops in reserve, unless they had a sudden bout of stupidity.
If we launch an assault on the Under-Citadel only, it's likely those reserves will be sent against us. I'd argue that a full assault on the Under-Citadel coupled with a raid-and-withdraw on Under-Karagril would be best. No matter what kind of reserves Mors has they can't be everywhere at once and Under-Karagril being overwhelmed and becoming a highway for endless hordes of Greenskins right into the Under-Caldera would rather be more threatening than the Under-Citadel being taken by the Dwarves, which would commit the reserves to Under-Karagril.
Result:
- The Under-Citadel assault would contend only with the Under-Citadel defenses and no or lesser reinforcements, which would make things easier.
- The Under-Karagril defenses become a much bigger problem for Mors and they have to commit their reserves there, not to us.
- Whether Under-Karagril folds or not, things would be more advantageous for us: if they hold, the reserves will need to be committed to it and will allow us to set up defenses. If they fold, the Green Tide would be attritioned by the Mors defenses, the Mors reserves and would attack a Dwarf Throng that has retired behind a defensive position in Karagril and the Karagril-Lhune Underway with Kazador and a Runelord, which would be a viable position. Under-Karagril would still be unoccupied and Mors, with their chronic lack of territory would likely extend there next turn to recoup losses rather than attack a fortified dwarven position in the Under-Citadel, especially after the losses they would have suffered during the assault against Eshin.