Wait

The ML's son is the brown haired kid. The MC's son is the black haired one in the 1st chap. In the future, as per mc's sister writing, the two sons get married(๑•ㅂ•)و✧ "but isn't that like incestuous since ML and MC would end up together?" Yes, but in some way no? because MC is not really on the right body, we can't really straight say it. And who knows, maybe the child is the child of his ex or whatnot

And the ML isn't already married into the MCs family in some way?
I thought he was married to his sister or something.
Idk I swear my brain got yeeted together with truck-kun.