My childhood was blighted by my Mum’s alcoholism. Personally I wouldn’t let him near my child. The unkind comments will stay with your son possibly for the rest of his life. Your FIL is an adult and will only be helped if he makes that choice. Your son is a child and needs your wholehearted support.
The problem is Christmas can be an awful time for those living with an alcoholic. What is likely to happen if he persists in his nasty behaviour to your son? Would he leave quietly if you told him to go or would there be an almighty scene? Would your OH have to go with him? Is it possible to have a conversation with your son and ask him how he feels about grandad’s visit?
What if the family visit grandad on Boxing Day or during the break before New Year. That might ease your conscience. If he is rude you can then just walk out and leave him to it.
Alphabetical girls and boys names January 2024