It would bring me to the point of nausea. There are lots of things which I know very well happen, but that does not mean that I want to observe them.
Hmm..are you the same person who posted on another forum they wanted to screw their aunt who raised them and is considered their mom? Eh? lol. Did she encourage this in some subliminal way with the pretense its not? Like for instance she wont get a man herself so she poured her attraction onto you because you are safe. Wasnt her biological father also a pedophile?
This is the situation you are NOT in? Then, no, it doesn't help. Your notion of what trumps* what is not the operative factor. The value system of the protagonist is. Whether the grandmother has any right to a heart attack on hearing of the incest (or whatever) makes no difference to how the perpetrator rates committing the incest vs losing the grandmother. If the law doesn't cover a situation, the issue becomes all about value judgments of the actor. *You know we'll have to purge that word from Oxford, right?
At the time of writing, the OP had not come forth with specifics. I was considering such possible issues as the OP's sexual orientation. It would be unfortunate if the OP decided s/he couldn't be his/herself because his/her family members might be emotionally unable to cope.