Sweet Siblings

Rarity and Rainbow were relaxing on the couch together, long ago Rainbow had asked Rarity to be her "pretend girlfriend" but quite a while afterwards they had acknowledged that the "pretend" part had vanished and they were now legitimately dating each other properly.

Whilst they were relaxing, their daughters, Rainshine and Glittergloss, walked in to ask their mothers an important and interesting question.

Rainshine, addressing Rainbow, said "Mom, know how I'm your daughter and half-sister but aunt Twilight helped me get you pregnant with a baby that'd be my half-sibling and child but also your grand-child?"

Rainbow went "Uh... yeah?"

Glittergloss, addressing Rarity, continued "We were just wondering if maybe you'd let Rainshine and I get each other pregnant as well!"

Rarity shrugged and said "Why not? I'll call Twilight tomorrow OK?" Rainshine and Glittergloss high-fived each other and left the room.

Rainbow chuckled "Sibling lust! That reminds me, how did you and Sweetie Belle end up having sex with each other? Care to tell me?"