Thanks! I get what you mean, now. I agree, if they're not sharing genetic material, even if they perform the same function as each other in each universe, it's definitely not incest or selfcest. My understandings of incest (both the literal definition of the word and my more inborn reaction to the idea of it) is that similar genetics is a necessary if not sufficient condition.
So this two Bs have some same genetic material. So they are from genetic point of view are half siblings.
I feel like the fact of being from different universes changes this. I don't know why I feel this way, but for some reason I don't get the same feeling of familial relationship between the two. (for clarity's sake, I will use Loki has a name placeholder) Like, assuming genetics work the same between both universes, and Loki's mom has the same genetic material in both, and in universe 1 she marries A and in universe 2 she marries B, and in both cases they are the respective biological father of Loki - like, I understand that genetically the Lokis would basically be half siblings, but I definitely wouldn't consider them related at all and wouldn't consider the relationship to be incest. Though if they were capable of reproducing with each other, they would probably have some genetic issues.
It feels more like in that case the genetic similarity is an accident of large numbers, like doppelgangers who look almost identical despite not being related at all. I think there might need to be some of the familial dynamics to it, at least for me. Which does I guess means that while similar genetics are a necessary condition for incest, they're not sufficient.
Re: SA
I feel like the fact of being from different universes changes this. I don't know why I feel this way, but for some reason I don't get the same feeling of familial relationship between the two. (for clarity's sake, I will use Loki has a name placeholder) Like, assuming genetics work the same between both universes, and Loki's mom has the same genetic material in both, and in universe 1 she marries A and in universe 2 she marries B, and in both cases they are the respective biological father of Loki - like, I understand that genetically the Lokis would basically be half siblings, but I definitely wouldn't consider them related at all and wouldn't consider the relationship to be incest. Though if they were capable of reproducing with each other, they would probably have some genetic issues.
It feels more like in that case the genetic similarity is an accident of large numbers, like doppelgangers who look almost identical despite not being related at all. I think there might need to be some of the familial dynamics to it, at least for me. Which does I guess means that while similar genetics are a necessary condition for incest, they're not sufficient.