Well you can say that if you view maybe view it in legal term or when it comes to law.
Well in real life it'd be weird, but hey this is just fiction. I'm not a liberal or anything, I honestly think incest is fine if they're both consenting adults. Just not having a child bc of genetic mutation of course, and also if one member has power over the other (thereby abusing) and also sexual grooming. I guess incest but not including parent x child. Also cousins can get married with one another since it doesn't cause genetic mutation, and it's the norm in other countries.
I mean I don't love my siblings and cousins romantically and sexually, I just think incest doesn't deserve this much stigma since the problem with incest is mostly your kid getting genetic mutation. Parent x child can go die in a ditch anyways.
Is it still be considered incest even if they're just stepbrothers? ಠ_ಠ