I'll try to keep this brief - DP has an older stepchild, they dont live together. SC has constantly been in trouble, doesnt work and I dont think is a very nice person. They are what I would call abusive to DP, manipulating him emotionally and only ever in touch when they need something. They didnt send him so much as a text for Father's Day. I dont think they have a problem with me.
However, my mother has always had a difficult relationship with her stepchild. DM is not an easy person so I can understand they found her hard to accept and have been pretty unpleasant but I can see both sides. Bottom line she and her husband barely speak to them and he has written them out of his will. It has made life quite difficult for him.
My relationship with DM is complicated and I tend towards doing the opposite of what she does - not to be awkward but because I think she makes bad choices and I rarely agree with them.
Because of the situation with my mother I am really torn about SC. I dislike them intensely and hate how they treat DP. I want nothing to do with them but I feel DP needs support and I dont want to put him in a situation of having to 'choose' although they are really damaging him. But I can see how it has affected my SD and I dont want that for DP, or to make his life any harder.
Any advice on trying to do the right thing? I'm always unsure because of not wanting to be like my DM but I think the 2 situations are quite different.