I recently cut 2 toxic relationships out of my life completely. My father and my sister.
I had put up with their constant undermining, disregard and neglect for my children, sense of entitlement to my unconditional love, giving nothing in return, fair weather support, and constantly being shamed for being fat.
The last straw believe it or not, was last summer, when they separately invited them and their families to my house for a cheap summer holiday and on top of stressing me and my lovely husband out, were unkind to our beloved dog. That was it.
I never realised how much space they took up in my head and how their critical voices constantly undermined me.
Now I feel like a different person. The people in my life are beloved friends and family who I would trust to be kind to my dog, and who love me, warts and all.
I'm sorry that your FIL is grieving and drinking too much. But it's not your circus, not your clowns, you can indeed tell him he's not coming and the reasons why. It's hard and scary, and you'll feel really guilty. But over time you will feel empowered as a mother and in your own home.
You never know, he might start to make a real effort if he knows his awful behavior will not be tolerated.