I'm having the same issue too! Gave Tarquin both parts. Now he's stuck in the graveyard, and nothing will move him on. I've got nothing left to do in Act II.
Malady warns he wont join the ship if I leave like this. (I tested; if I leave he indeed does not join the ship.)
Hopefully this can be fixed! Feels super broken not to be able to carry a main NPC with me as obviously designed.
