Slime_king
honestly i really think you should've let the mc impregnate her while making his uncle think its his son, not the sperm donor excuse but just tricking him into thinking that "he" really is the father and that's really his son. Like you could've give him that potion so that he really think he can impregnate his wife with it except the potion is just a scam and mc already impregnated the aunt, and when the uncle and the aunt did it, the uncle will think that he successfully impregnated her thus making him think he's gonna be a father and when the aunt told him that she's pregnant she can say its his child except its not as its mc's child.That will fulfill the uncle's dream thus making everyone happy and i also think this is less weird than what you did but its your story so ¯\_(ツ)_/¯
Sigh. I thought his first child would be from grfyia, but he went and impregnated someone who was not from the harem. The downside is that his kid won't know who his father is. Imagine you are the strongest person in the world and you go and make your child look like someone else's child. It is really one of the biggest factors that will drop the story. I think I'll leave it too.