Yes, you can sign with that. Hardware wallets don't care about your gap limit, they aren't deriving individual keys when you setup the wallet. Rather they just store the master private key (or the seed used to derive the master private key) and then derive the individual keys needed on-the-fly. So if you tell it to sign with the 999,999th key, by giving it ...
I accidentally swiped my bitcoin into a watching only wallet in electrum ... from a paper coin
The way you describe this makes it difficult for me to work out what happened but I am unfamiliar with Electrum so it may make sense to someone familiar with Electrum.
A Watch-only address is a bitcoin address for which the wallet has no record of ...
You have a malware version of electrum. Did you update it recently because you were prompted to do so by in app popups? Check your browser history for the download URL. electrum.org or download.electrum.org are the only legit places to get electrum.
Not normal, each cosigner should have a unique master public key.
There is a reported bug in Electrum 3.3.6 that causes the issue on macOS.
Until a fix is pushed to production, it’s possible to get master public keys using the Electrum console (View/Show Console).
[k.xpub for k in wallet.get_keystores()]