I don't wonder about the sexual lives or personalities of family members. I couldn't tell you what others do. My understanding/experience is that it's not considered common or normative to think of things in the terms you mentioned, but that doesn't mean other people might not. Personally, I am not curious about that. Having these private thoughts, though, you're not hurting anyone, which I always consider the deciding factor as to whether something's alright or not.

(And I'm a mid-30s female who considers myself very sexually liberal, for context. I've had experience in peer-counseling around queer and alternative sexuality and sexual practices and worked through sexuality-related issues in therapy.)