Actual incest... not my thing either.
But the incest tag here also applies to those not related by blood...
So, I'm generally ok with those VNs as long as it's structured, appropriately...ie, no reader/MC LIs/sex partners are blood relatives...
Very, very distant cousins, kind of a gray area...
Otherwise, step, adopted, no blood relation...an aunt who isn't blood related...I'll allow it...
Oh, and doesn't bother me if other characters in the VN engage in incest, like twin sisters or something, having a threesome with the MC... just, don't let them be blood related to the MC that I'm supposed to be playing as...

Oh, and the clone thing, another gray area... Yeah, looking at you Chasing Sunsets...