Sister in law trouble

Myself and my partner have put up with years of my sister in law doing ridiculous things that have cause us hurt or anger. She recently met a man and they've been going fast in sense of house babies etc. He seemed nice and we all got along fine. However in recent weeks they came to my partner (her brother) and demanded help with something in their personal life. They didn't listen to his advice and then they blamed him when something went wrong. They were completely out of line especially her partner and my fella wants no more to do with either of them. I for some reason am feeling guilt with his decision because its family. Altho I know he is right. Is it wrong to cut someone out for good?

I have recently severely restricted my interactions with my family. Years and years of drama and verbal abuse have led to this. The final straw was when they started cussing at my wife. Sometimes I regret how little contact I have with them, but my life has become a lot more peaceful lately and I am in a better place as well. Just because people are blood relatives, does not give them the right to behave in such a manner. My advice is to try and not feel bad. Your job now is to back up your partner, and support him. If this is what he wants, you should be supportive in that.