You'll need them to be able to use 2 out of 3 sets of seed phrases.
What I mean is that he has the seed phrase, the seed phrase can be used to always setup the wallet and spend from it. It is true that the public key is needed for to make transaction, but the seed phrase can always generate the public key and the private key needed for spending.
Then you're turning your 2 of 3 into a 3 of 3. Imaging one of the seeds is in a safe deposit box in another country.