Golden Baby

A golden baby is when a child in conceived by a lesbian and a gay man. The man and the woman are usually friends and it is always consensual with the woman’s partner. The man cannot be bisexual for it to be considered a golden baby.

“Wait, you’re having a baby? Did you cheat on Katie?”
“No! Nothing like that. You remember Alex?”
“Yeah.”
“We’re having a golden baby.”
“Alex’s husband was cool with that?”

Oopcest

Oopcest is when two consenting individuals of a reasonable age for each other have sex and then later learn that their parents are romantically involved and getting married. When their relationship began, it was not incestual, but once their parents are married, it is oopcest.

It is very common in anime and manga romance.

"Rui and Tsukiko had sex. It was fine. Then their parents got married. That's some serious oopcest!"