Hi Zhong,
Yes, pls spay ur mom-dog to prevent future pregnancy. There is no "unexpected" pregnancy - as long as they are not spayed/neutered, u have to expect pregnancy.
I have heard many times that spaying/neutering is inhumane. In fact, it is just the opposite. Pls go to this site for reasons why:
https://www.aspca.org/pet-care/top-1...euter-your-pet
As for ur current dilemma, it ur intention is to find them a new home, then u need to look for adopters, not fosterers. Fosterers will care for d dogs temporarily n u wil eventually take d dogs back. But it sounds like u totally cannot keep them anymore so u need adopters.
U may want to list d three pups separately. N clearer photos of each will help. Description of each pup's good points will also help. Good luck!