I do hope that Mum will return, poor mite.
Pinot, you're doing a fantastic job and should be really proud of yourself. So many people would have just ignored the cat or worse. I hope karma rewards you handsomely. :)
If and when Mum returns I hope that in time you might be able to find her a home (or keep her!) - CP did have a scheme going whereby they were offering free neutering/spaying and even if they no longer do they may be willing to help under the circumstances... it's well worth asking as otherwise she will just get pregnant again very soon. If they can't help please come back to me and I'll do my best to find an organisation which can or to appeal for funds with my rescue friends to help with the cost. Likewise with finding Mum and/or kittens a homechecked, responsible home if needed.
Likewise, if the vet has charged you for the care so far provided/will charge you for care of the little family, please pm me and I'll try to appeal for help with your costs. We're all struggling to feed and care for our pets and children as well as help rescue cases where we can but I wouldn't like to think that you are paying for it all yourself and if I can help, even if only with a few pounds, I will.
How's the poorly one doing?