family trouble.. opinions?

I'm to keep a long story short my mother came our as gay 5 years ago which went on the end her 2nd marriage to my stepfather. my stepfather never had anything to call his own so he arrived to my mother's house with a black bin bag of clothes and he left the same way. my step dad loves my older son who is 10 and still sees him every couple of weeks for a few hours, my son calls him papa. he has moved on in his life and has met a woman and has a 1 year old kid now. we all keep it cival but I don't particularly like the guy. anyways thismorning my mother rings me crying saying she has received a solicitors letter and my step dad is demanding my mother's house to be sold and half the money given to him.. my mother has her business in the house and works so so hard to pay all her bills (most of which he ran up) and she is devastated. my problem is do I continue to let this low life piece of shit continue to see my child or cut ties ?? just to add this is my mother's house which he moved into, he ran credit card debt up before he left which are just paid off now and my mother has been trying to pay him monthly outside of court and has paid €5000 So far with an agreement they came to last year