What would you all do? Bare with me this is a long one.

At the end of July this year I held a 1st bday party at my house for my lg Lilly. I invited all her family and friends and nobody said they had an issue with anyone coming. Everyone was aware of who was invited. The next day the mil rings up and starts a row with me over her ex coming (my oh calls him dad as he brought him up from small) and her dad (my oh grandad) been forced to be in the same room. My oh grandad sat for several hours talking with my oh dad, they even shook hands when they left. I told her (she lives in Canada) that I would invite who I liked into my house it wasn't her call to make. If she was in the country my oh dad has said he would out of respect for her feelings stay away from the house if that's what she wanted. Over the last few months she's rang my oh up shouting/swearing/ranting/crying at him. It's all my fault apparently I should of took her feelings into consideration. She's used my kids against me (4kids to 2dads) and now deliberately treating them all different. She's back stabbing me, she's contacted my ex (older twos dad) to gain dirt on me to throw at me, she's told me I have to let my kids go to their dad (court order stopping contact ATM) etc. Last night came after if been in court for the kids again and she asked my oh how it went and I asked him not to talk to her about us again. She didn't like this and went off her head at him saying I'm changing him, I'm the devil in carnate, I'm coming between him and her (I've told him to have a relationship with her she's his mum after all), she hates my guts etc. My oh suffers with anxiety quite badly and we had it under control until all this and now he's physically ill with it. Any advice?