I am trying to find a title of a movie. It starts where this vet is hitchhiking. He gets picked up by a family in a VW Bus. There's a father, mother and a baby.

He takes over the family. Runs their lives. I think he killed the father. I think he forces the son to have sex with the mother. Because there's another kid. And the Vet can't have kids since he was wounded in the war.

Then Kathy Bates ( I think it's her) shows up and take charge and rescues the family.

I check online and can't find the title.

Please help.

When You Comin' Back, Red Ryder? (1979)
IMdb review:
Most descriptions of this movie read something like "psycho Vietnam veteran terrorizes roadside diner patrons" or "bad movie adaptation of Medoff's stage play", and, though these may be accurate surface descriptions, the movie deserves far more comment than that. As the movie progresses, each character's deepest motivations and fears are revealed and what is exposed is the shallow values, ignobleness and dark fears of mankind.
Marjoe Gortner's youthful rage manifests itself strikingly as he rants on at each of the diner patrons. His cynism is directed at pretentious city intellectuals (Hal Linden and Lee Grant), smalltown folk (Stephanie Faracy), self-righteous do-gooder (Pat Hingle), bad--wannabe (Peter Firth), and even the protagonist's girlfriend (Candy Clark). The film gives a whole new meaning to the American perception of machismo, and much of this can be difficult as well as fascinating to watch.

Kathy Bates isn't in the film, but Anne Ramsey is. It's possible you mistook a young Anne for the other actress.

When You Comin' Back, Red Ryder? (1979) - IMDb


You could check out much-younger Kathy Bates in "Come Back to the Five and Dime, Jimmy Dean, Jimmy Dean" (1982).
IMDb synopsis:
The Disciples of James Dean meet up on the anniversary of his death and mull over their lives in the present and in flashback, revealing the truth behind their complicated lives.

Come Back to the Five and Dime, Jimmy Dean, Jimmy Dean (1982) - IMDb

Her co-stars include Cher, Karen Black and Sandy Dennis. There's no connection; I just threw in this one because it gets overlooked, too.