I assume you have told your mum and gran how this is affecting you ? If not do so ! Then you have to take a step back and tell them you cant cope with it do dont want to hear about it, tell them you have things in your life to deal with and dealing with their games is just too much for you.

If your mum or gran creates and has a go at you do the adult thing and walk away.

Everytime they go to do somthing out of order just say 'I dont want to hear it' and walk away.

It is not for you to deal with its their problem not yours.....