Poor thing. I know how you feel as I have a sister with a mental illness who ruins everything. There was the threat that she would be there this Christmas but as it is my sons first Christmas I agreed to go with conditions that if she starts she leaves and nobody is to comment about her looks or behaviour (anorexia). Thankfully she decided not to come.
Could you make rules to keep things civil? I would still go for the kids TBH.
Hope it works out
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