Really not into the piss, but otherwise really nice and sweet, not the thing you usually find on this site.

Some ideas:
A large group composed of sets of siblings(part of a club for siblings that want to be slaughtered together?) come to volunteer, having heard of the humane treatment and thus deciding it's a good place for their butchering.

In the future, when they've been helping out at the shop for a while, it's been a busy day for customers, and a slow day for volunteers. Maja, Moa, Erik and maybe Linda decide to join as volunteers on display, out of support of the shop and Evelina and because having been around the shop so long, they're okay and aroused by it, though they wouldn't volunteer normally. They do end up surviving through the experience, and they discuss what it was like(in the middle of sex, obviously), and while they enjoyed it, and wouldn't mind doing it again, it's not something they seek out.

Perhaps combine the two, with them being saved by the arrival of the large number of siblings coming to volunteer.