Sadly, CL is a cesspool of wannabe rescuers who don't know what they're doing, scammers who want free puppies to sell, and worse. For future readers, TRUST NO ONE on CL without doing significant due diligence.
Hopefully OP was responsible about it and didn't just hand-off the litter to a stranger without a background check just to be rid of the pups: he or she hopefully checked the 501(c)(3) status of this unknown all-breed rescue, called the rescue's vet to get a reference check on quality of care they provide (as any legitimate rescue would encourage you to do), and inquired as to community reputation with other rescues, shelter directors, etc (again, legitimate rescues would be happy to provide community references, as we have worked hard to build goodwill). Hopefully he or she also read their adoption contract and adoption qualifications (speutering contract, taking the pups back if it doesn't work out, training requirements, quality of placement, home checks, etc.), so you have peace of mind that they'll place the pups well and handle returns so that they don't eventually end up in a shelter.
There are some dumb all-breed rescues who see "possibly purebred puppies" and think that a money-making fundraiser fell into their laps. They don't know what they're in for --- and quickly get overwhelmed.
It's too late now, but when OP talked to the rescue's vet (you did that, OP, right?), there should have been a plan to get these 12-day old pups through this dangerous period without their mama, and a discussion of this foster's track-record with bottle-fed litters. When there are orphaned litters, this sometimes happens, but often some of the pups don't all survive bottle-feeding....which is why we move heaven and earth to find mama....one rescue I know even went looking in shelters for a lactating F who lost her litter to be a "wet nurse" (after a neg parvo test and careful temperament screen), as it increased the odds of the litter's survival (and she was fab with them).
That was hopefully all discussed with the rescue's vet and OP, so OP and the rescue made an informed choice ...for some reason, their vet thought was really important to "orphan" this litter....surely no one would separate mama and pups like this without talking to their vet about what's best for the pups. Even in shelters when the mama is feral and can't be handled and has to be separated from pups earlier than anyone would like, it's the shelter's vet who makes that call. Right, OP....?
Last edited by Magwart; 08-27-2017 at 12:12 PM.