I had a similar problem with one of my most precious cats (RB now ). When Titti was younger she would sit on anyone's lap, that lasted until she turned one. For her remaining 17 years she was very affectionate with the immediate family but she hated everyone else, to the point of being almost dangerous. She made only a couple of exceptions but that was it. We could only make some vague supposition on what could have caused it.

Sorry if I can't offer any advice!