If a woman is due on October 12th and they had sex on Jan 4th then she slept with someone else on Jan 19th who’s most likely the father?

He says she has pcos so there’s no way to know when she ovulated but she’s only due 8 days before me and the dates lead me to believe the guy from January 19th is the father. They will do a dna test but he wants to ease his mind. Any advice??

I’m due October 20th and I got pregnant between the 22nd and the 26th so there’s just no way she’s due 6 days after me and conceived the beginning of the month right? I don’t want to steer him wrong