Okay, think of it this way.
Your family members, right now, all have reproductive organs. And primary and secondary sexual characteristics.
Do you regularly fantasize about those, and incest? Because psychologically, we're programmed by our own wetware to not feel that. Like, if you start to try, your body gives you a bad taste in your mouth (metaphoric) and it becomes gross.
Even though, objectively, they shouldn't. Because if we were to pretend aversive programming didn't exist and was valid, we'd see siblings and parents and extended relations as potential fuck partners. And most do not. But they're just as capable as any other person to have sex.
Does the thought disgust you anyway? Do you just NOT see family in that light?
Then it's the same if they embody some other fetish you have. You go "Ew" and compartmentalize the thing that is hot, or cool, and get the family member out of that equation.