I took what I know to be valid xpubs from my three keys and used the derivation path for nested segwit. However, I can't sign from that quorum. I'm thinking this is probably because the xpubs I am using were not generated by the derivation path I specified?
Perhaps.
If those Nested SegWit extended public keys are derived from your master private key with
m/49'/0'/0' path,
But used it in a MultiSig setup and provided the standard path of
m/48'/0'/0'/0', then your hardware wallet will derive a different xpub key than what you've provided.
What does the descriptor looks like? You can edit the extended public keys for privacy reasons.