When i created the multisign wallet I had generated a new seed for the first cosigner whereas for the second when it asked me to insert the master key, I insert the key from a 2 factor authentication wallet master key to which I do have the seed to that wallet too.
2FA wallet is different from multisig wallet. If you want to use a multisig wallet, you will need two wallet for 2-of-2 multisig. Using Electrum wallet as an example:
On each wallet (the 2 wallets for the 2-of-2 multisig wallet setup). Open and name your wallet and press 'next', you this image will appear:
Click on multisig wallet (not wallet with two-factor authenticator) -> create new seed -> paste your seed phrase -> paste the public key (or seed phrase) of the first wallet on the second wallet and that of the second wallet on the first wallet to setup the 2-of-2 multisig wallet.
Note that it is 2-of-2 multisig, meaning that you will always need 2 signatures for making transaction. Backup your seed phrase separately in different locations and have the replica of each also in different locations.