was Doris really the biological mother of Jimmy?

I know that we are supposed to believe that the baby who was kidnapped 19 years earlier was in fact Jimmy and the biological son of Doris.

However this doesn't fully make sense to me. Doris seems to show absolutely no maternal interest in Jimmy at all. Doris has been on some kind of a mission for the last 19 years. What doesn't make sense to me is that her mission seems to be solely about revenge. Yes, her husband was murdered so I can understand that revenge would be a part of it for Doris.

But it is very hard to see why Doris would have no interest at all--it would seem--in reuniting with her long lost son. After 19 years, she has finally--through her PI--tracked down the town where Jimmy lives. And yet at no point does she make any effort at all to track Jimmy down. This makes no sense to me. She didn't willingly give up her son for adoption, her son is still alive, and there is absolutely no reason why she should have lost any maternal feelings for her son.

It is all about revenge and not even a little bit about reconnecting with Jimmy for Doris, and this makes no sense to me if he is her son.

I personally think there is more to the backstory than is revealed--and that will probably always be a mystery--but I also think it is possible that Kate really is the biological mother of Jimmy. Except when she is being forced to engage in what appears to be incest, Kate shows far more in the way of maternal concern for Jimmy than does Doris. Despite the incest, for all meaningful purposes, Kate is the real mother of Jimmy, not the stranger from the East Coast who shows no interest in even knowing Jimmy.

Watching the movie again, including some key scenes with Doris, makes me think that Jimmy's actual biological parents are Kate and Doris' partner who was murdered 19 years ago. I've forgotten the name of Doris' partner so I'll call him Mr. Knight. I suspect that Mr. Knight and Ray knew one another before they picked up Ray, but Doris didn't know this so they played dumb.

Doris comments to the police that Mr. Knight, although not military himself, had a lot of respect for those who served and felt he owed veterans, especially Vietnam veterans, something. I suspect there is more to Mr. Knight doing favors for veterans than just picking up the odd hitchhiker. I believe Mr. Knight, similar to Jimmy later on, was recruited to impregnate Kate because Ray couldn't do the job himself. That's what is really meant by Mr. Knight doing favors for veterans because he felt he owed them. Then for unspecified reasons--and it might have been the subject of some dispute--the Knights rather than the Wests end up raising the kid at least at first.

This is a big part of why Ray murders Mr. Knight. Ray is conflicted about other men being sexually interested in his wife. Because he cannot do the job himself, he sometimes enjoys watching other men with his wife, but it makes him jealous. Notice that the stranger in the bar expresses attraction to Kate early in the movie, and is soon killed by Ray. Jimmy is forced to have sex with Kate, but that makes Ray jealous, and Jimmy is later severely beaten.

When Doris tells Kate to say "silence is not golden", it seems that she knows much more about Kate's history than she previously let on to the police. It also doesn't make sense to me that Kate would agree to raise a baby who wasn't her own and who had been kidnapped. There are sometimes stories in the news about people kidnapping the babies of strangers to raise as their own, but these stories usually involved infertile woman. In this case it is Ray, not Kate, who is infertile and I'm sure Kate would opt for an option like artificial insemination over kidnapping a baby.