DD's sperm donor did this with his older two kids. He favored the athletic child over the artistic one. He only became interested in the artistic one when the artistic one became athletic. It was very obvious and very bad. Sperm donor ignores DD completely.

The only advice I can give is find out why he does it and see if you can change it. No matter what document his favoritism and if necessary go to court and see if you can cut or limit his contact.

My husband has three biological children. All in their thirties. Two boys and a girl. Well two men and a woman. You would never know he had sons. His inky concern is the spawn of Satan daughter. The saddest part, his sons know they mean nothing to him. The awful part. The spawn of Satan knows she is daddy's special child. She did well, Italian father, only girl and youngest child. Talk about a recipe for disaster. So I guess it happens more frequently than we realise.

Yes, my husband also has 3 children but puts all of his time/care/attention into the oldest daughter. Like you, stepbell, I have tried pointing out how unhealthy this is for his other children but, like you, my husband just doesn't get it. He literally doesn't see that he's doing it.

How I handle it, is to take care of the other two - just pamper them and love them extra. They love it and they love me. Frankly, I stay in this marriage for them and for my own two. I'm like a single mother of 4 while DH, oldest SD, and BM are a separate family unit.