Where does your partner stand on all of this? I had problems with my MIL and struggled with DH's constant defence of her bad behaviour. It took him a lot longer than me to realise how her behaviour was affecting us individually and as a family, and now we are pretty much 'on the same page'. This, to me, is key. It's their mother. They have a far longer history and you don't want to ostracise your other half over the MIL.