Family altercation with future wife & mother and I'm caught in the middle

Hi all,

I'm at a loss, and I'm losing sleep over the current situation that I'm in so any advice or help would be greatly appreciated. I often find myself finding the best advice from random people over the internet that can relate. This is sort of a lengthy one as well, my apologies.

Where to begin.. My wife and my Mother do not get along at all. I have a Mother who is a very toxic woman, and a nuisance when it comes to my children and my life with my Fiance. My Fiance and I have a steady good job, a healthy relationship, and essentially zero problems except one... (my mother).


Now how this began: I would pay my mother to babysit for us, and she said I could always rely on her to watch the grandkids... well one day she abruptly decided that she no longer wanted to do this anymore due to her health. Then she decided abruptly to move to a different state with her significant other, with no two weeks warning or heads up for us to find someone else. Now keep in mind she is a very good Nana, and loves her grandchildren very much, but how sudden everything happened it really upset myself, and my fiance because we then were scrambled to find someone to watch our kids during the COVID-19 crisis so we could maintain our jobs.

Following this further, I let my mother know how I felt, but my Fiance really went at her logically, but my Mother does not handle confrontation well and took her as a threat. Lastly, before she left she threatened to call my fiances job (because my fiance likes to smoke weed from time to time for anxiety purposes). One altercation led to another, and now my Fiance decided that she no longer wants my Mother to come to the house. (rightfully so). I spoke to my Fiance about boundaries, and the fact that I was still trying to make this work for my Mother and the grandkids & she was appalled by it; saying I didn't defend her, and I'm just open arms to my Mother.

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So now that you know the situation, it only gets worse. My fiance was going to leave me over how fast I forgave my Mother or tried to let her see the grandkids during the month of May. I would cut my Mother off, however she has a good relationship with my children. Now, my mother then moved for the month of June, and me and my fiance were then fine and worked out the kinks between us and were happy she was gone. She also knows I talk to my Mom through facetime or I facetime the grandkids... she has no issues with this, but now my Mother is returning home because it didn't work out of her significant other and is wanting to see the grandkids again and is in our lives again. I want to respect my fiance, but to be honest I am worried that if she tries to keep the grandkids from my Mother, my mother will do drastic things to make our lives a living hell & actually act on trying to get my girlfriend fired from her job, or showing up to the house unexpectedly not respecting boundaries. How would anyone approach this situation?

Thanks for taking the time to read this anyone.