You are so far behind in this game, player. Dev introduced fan service some diverse cast members from her other game and made some more pandering small apearences of new unexplored guys to pander to this fetish of yours in the last updates - there are a lotta guys and Lena would deffinitely lose count of who and when got inside her - so many fetishits around this thread spinning their theories, easy to lose count of who did it when and who might the child resemble.
Nah, the real plot twist that the dev is going to pull in the end is that Ian is still the father of Lena's black kid. We will find out that Ian's mother actually got fucked by a black man, and she got extremely lucky that only her whiteness expressed in Ian, so her husband never became suspicious. But Ian still has that black gene in him and it, extremely unluckily, expressed to his child with Lena.
This will satisfy both the vanilla and ntr groups, as Ian didn't get cucked by having Lena be impregnated by somebody else, but still ended up raising a black kid, unless the vanilla group is racist against black children of course.
This is also a thematic ending for the game. Ian's mother got so lucky that Ian looked like a regular white human, but to balance that luck, Ian got so unlucky that he got a black human with another white chick, a la 'Our Red String', strings of fate connecting them.