Can I let my partner seat guests but not move the tables?

Yes. Choose Lock layout in the editor’s header. While it is on, editors can seat, move and unseat guests, but the tables stay where they are: nobody but the owner can move, add, remove or resize one. Choose Unlock layout to open it again.

The lock is for a finished room. Set the tables with the venue, lock them, and hand the seating to whoever is helping.