My DH has one sibling and they are awful, as is their spouse. There's a huge backstory that I won't bore you with but basically almost everyone who knows them is no longer speaking to them. On the contrary I have no other people who I don't get on with!
For years I have generally avoided them. DH's family is very fragmented and there are no 'family occasions' so I don't have much cause to see them. My husband visits very occasionally, maybe twice a year. My MIL is an intelligent woman who is interesting to talk to but she enables their behaviour. They moved in with her about 2 years ago so that has made things more complicated. One of them works, the other has never worked (at all) and MIL doors the bill, and has in fact gifted them her house. This has caused huge resentment but only from me, my husband is just saddened by it.
I'd like to never think about them again, but it's hard now they are living with MIL. Of course I want my husband to maintain any family relationships he wants to, and I want to continue some sort of relationship with my MIL who I have known most of my life so it's slightly different to your typical MIL/DIL relationship as it isn't solely around my husband. I just want nothing to do with them. I don't want to think about them. Every time they pop up with some sort of grabby request, it just gives me so much rage that it's not healthy. How do I manage this? I am not a confrontational person so it just simmers. They have children who I have only met a couple of times, they do know my husband (but much less than our nieces and nephews on my side) and my husband has never received a thank you for birthday/Christmas gifts (which I do try hard on even though I don't know them, it's not their fault). I just want to say that I'm done and if he wants to continue to buy them bits that's fine.