It is kind of confusing me because to me it is still 2-of-3 multisig wallet in which only two seeds are need to make transaction, not three seeds.
You need two of three seed phrases for signing a transaction, but to create your wallet, you need the master public key that is derived from the other seed phrase too.
You create a 2 of 3 multi-signature wallet, so that you will be still able to spend your fund even if you lose one of the seed phrases.
In the case you haven't saved the master public keys, will you be able to spend your fund if lose one of the seed phrases? Can you generate your addresses? Note that before signing and broadcasting your transaction, you should create your wallet.