WOW-read it so differently.
Had a baby-bio child of my "secondary". The three of us are raising her together. She calls Maca (my primary) "daddy", but everyone in the family knows her genetics and it's not going to be a secret from her either. She's only 2 so she doesn't UNDERSTAND those details yet, but we don't lie, hide or pretend.
she's happy, we're happy....
IT REALLY depends on the details of the people involved how you handle it...
"Love As Thou Wilt"