Reinstating Family Plan/Migrating iPhone SE to Expanded Network

Hello! I recently purchased a new phone for myself and migrated it to the Expanded Network. However, when I did so, it broke my family plan with my father's phone. I'd like to get him back on my family plan soon, but he's on the old network. We just bought his phone this last fall; will we need a new SIM card to get it migrated over as well? Thank you for your time!