Hi, my name is SabrinaKD! Help with appointee, how will this affect our benefits?

Hi I am in need of some advice. My partner's mum is his appointee he claims pip and Esa which is paid into her bank. We are now thinking about moving in together. I claim universal credit. So we will need to make a joint claim. How do we do this with his mum being his appointee ? This is something he needs, and I am happy to become his appointee but again we don't no how to do this. If we switch who his appointee is will it effect our benefits? How long does all this take ? Would i need to become his appointee before we make a joint claim? From what i understand he wouldn't need an appointee with the joint claim because I would be able to handle all of this, it is the pip I'm concerned about for example if his mum gave up the appointeeship so we could make a joint claim how can I then give him the help regarding his pip? It's so confusing please help!!