In the Castle in TOTLM there is a dugeon portion that has 5 separate sections, each container different monsters, plus 2 "Stone Nuisances" that seem impossible to hurt. Has anyone defeated them (or is it not worth the effort)? I am stuck.

The stone nuisances are exactly that. They are highly magic resistant, but magical blunt weapons will damage them.

SPOILER:
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They will respawn after you kill them. But not until you re-enter the specific caverns where you find them.

Use magical blunt weapons to kill them the first time. If, for some reason, you need to go back into those rooms after they've re-spawned, use summoned monsters and shielded wizards to soak up the magic missiles.