I've read a few 3ps where twins share a single partner and never occurred to me that it ca...

I've read a few 3ps where twins share a single partner and never occurred to me that it can be incestuous (?) ... maybe because I think of twins as one unit(like a coin with two sides). But doesn't mean they are one entity of course, they have their own thoughts and personality. 3p BL's that I had read so far doesn't have that much poly-like definition(all of them love each other equally), usually, it's two tops sharing a bottom and the two tops are either twins, or bestfriends/friends. Rarely, the two tops had a history in the past till they met the bottom (a little toxic ngl). But overall, It never crossed my mind that it's incest