there are plenty of precedents where biological fathers adopted children who had other legal fathers presumed at the time of their birth.

Yes. But according to a couple lawyers we've talked to, they know of no case where the mother remained still legally married (and not separated) to her husband, but the kids were successfully adopted by the nonmarried biological father.

Doesn't mean such cases don't exist, but.

For now, we're holding off on any more legal action than what we've already done (we have a parenting agreement on file) and see what the future brings.