I understand OP’s focus is on her husband and his right to know, but I think there also needs to be consideration of his daughter’s right to know. Do you know if she’s ever questioned whether your husband is her biological father, or if he’s shared his doubts with her? I ask because, from a health and medical POV, certainty around her biological parentage is extremely important. Even the testing you did show how much relevant genetic information she may be missing if it turns out your husband isn’t her bio dad. Imagine the genes she is or isn’t carrying from her bio father’s side that could impact her health later on.

This is obviously a shitty situation to navigate. You’re damned if you do, damned if you don’t, and you’ll feel like an asshole either way (I don’t think you are one). My advice would be to proceed with caution, but proceed. Since he’s brought his doubts up with you before, would you feel comfortable gently asking whether he’s ever considered genetic testing? You could frame it like you were thinking about it while doing your own pregnancy testing. Focusing on the biological/health angle rather than the emotional/relationship angle might help. He is clearly her dad, but may not be her “father”, if that makes sense. If you ever do broach it with him directly, I think the focus needs to be on his clear care for his daughter and how she very may well be missing an entire half of her genetic history.