Dude, you focused on 1 sentence and missed the point.
#1 It is Your WIFE’S relationship. Stay out of it unless she asks for advice.
#2 Your wife knows her dad better than you do. Trust her.
#3 Biology does not make a parent. She believes her genetics is irrelevant to her relationship with her father. She’s probably right. Odds are that he’s suspected she’s biologically not his for a while anyway.
#4 He took the test, too. He knows. Knowing that she knows and is still seeking him out as though nothing has changed probably means the world to him. No need to confront something they both are ignoring.
#5 Your wife is a full-grown, functioning adult with a mature relationship with her father. She can make these decisions without your assistance. Quit it.
Also, if you undermine this and leak it in any way, she has every right to leave you. This could be divorce-worthy behavior.
Stay. Out. Of. Her. Relationship. With. Her. Dad.
Your comments in this thread make you sound controlling and judgmental, but I don’t think you’re trying to be. I think you feel strongly about this and think she’s making a mistake…but that’s the thing: This is HER mistake to make. It sounds like your wife wants time to process this, but you are pressuring her to tell him immediately. You are so sure she should be honest with him about this, you make comments about comparing her not telling on her mother’s affair results (her dad not fathering her) with her cheating on you. That’s such a low blow, I’m surprised you didn’t pick up on the controlling/manipulative vibe yourself.
I get that you feel strongly about this. But it is NOT your relationship and not your consequences. If she tells him and their fragile relationship implodes…YOU will share the blame. If she takes the time she needs and decides he can handle it, and their relationship implodes…she will not blame you for it.
Just listen to her, like really listen. Don’t listen for ways to argue that she should do what you want her to do…just hear her. Let her process this and make her own decision. She is the one risking her dad here, not you. Let her figure it out. Repeat what she says so she can hear it…don’t add judgmental tones. Just be there and let her do the deciding.