Cheating scenarios ain't really my thing, but can't help thinking, now that the siblings-in-law's switches have been flipped, they have no choice but to abide by the words of (the late) M.J.'s:
Heh, "Planting Seeds" indeed, right inside her sister.
I feel like this kind of plot fits for a cheating release, backed up because of a pregnant wife and her sister's husband isn't around.
That ending though, I wonder why they'd leave a crack in the door like that? It'd certainly make it easy for someone to...see what they're doing.
Home is where ever you want to be. Vaginas are my natural home, but i have a summer house in the butt and a cottage in ass pussy on girlwitdong island.
That's my hope for their relationship, but I'm not sure the younger sister is that type of character. Though, she's only in the story for a couple pages, so maybe? Older sister wasn't doing a good job of being discreet though! lol.