2 dads not possible

Is this in CAS? You should be able to make each sim the parent of the child? (Do it separately for each sim.)

I have had this issue in my game before, I was playing an orphanage and could not set the parent relationship in CAS or with the cheat using the MC Command mod even. Eventually, I was able to get it set up with cheats. You would search TwistedMexi's Sims 4 Cheat Resource. But, you will need his mod to make the cheats work most likely, this is since the seasons patch, unfortunately.

I'm not sure why you're having this problem @Taquanda. When I went into CAS to test the same just now, it easily lists both male sims as the child's father. In fact, I didn't have to tell the game to do so, it just automatically listed both as father. I know this seems like a standard answer only because it works so often, but do you have any mods that might be interfering with the function? Or maybe a game repair through Origin will help?

You have to set one as getting pregnant and one at becoming... So it makes sense. Weird!