If you view your restored 2fa wallet using a text editor like nano you will find the xprvs for 2 out of the 3 keys that make up your 2fa wallet. You will also see the corresponding xpubs. Since you know which xpubs make up your multisig wallet all you have to do is view the 2fa wallet file and copy the corresponding xprvs. You can then restore your multisig wallet using those xprvs and sign your transaction.

The location of your wallet files is  ~/.electrum/wallets/

I've attached a snippet of what you should be looking for: https://pastebin.com/11vsUuRf

Also update to the latest version of electrum i.e. 2.9.3 on your linux PC too. Otherwise you will face all sorts of problems. If you installed electrum using your distro's repos then first backup your wallet files, uninstall electrum using your package manager and then install the latest version using pip2 as per the instructions on electrum.org/#download. You can't rely on your distro's repos for electrum. It updates far too frequently for that. You have to install using pip2. In future updating will be the same as installing the latest version.