The Preacherbot technically couldn't marry The Robot Devil and Leela because Robosexual marriage was considered illegal until "Proposition Infinity".
The Robot Devil being obsessed with getting his hands back is questionable. Being a robot, he could easily get replacements. Not to mention, "Ghost in the Machines" shows him having a wardrobe full with replacement bodies for himself. Why not just take the hands of one of them or transfer himself into a new body?