Sickly litter of kittens w/ former feral mom

Well, I have a feeling I really can't do much to help, but just in case...
We are gradually taming and catching a feral cat colony in our backyard.
Our latest "catch" is almost two years old and only warmed up to us just
recently. She had a litter of kittens last July, only two of which we
ever saw. I have no idea if there were more, because we didn't see the
two until they were around six weeks old. We just last week coaxed her
into our basement, along with one of her litter from last year. They've
been actually very calm and not too crazy about trying to get out
(unlike her two siblings we rescued last year who bounced off the
walls!) So anyway, the mom cat was pregnant, and we believe they were
conceived around March 20th because we had a strange male cat hanging
around at that time. I wasn't expecting kittens for another week at
least, partly because of the timing, and partly because she hasn't
gotten very big.
Today we came home to find her with two dead kittens, and one scrawny
live one. By evening, she had another still born and another scrawny
one. I haven't seen kittens born in years (I believe in neutering,) but
these definitely appear underweight and maybe even underdeveloped. (Two
of the dead kittens had no fur.) I have a feeling they won't make it,
but they are crying a little and trying desperately to get milk. One of
them did manage to suckle, but I couldn't really tell with the other.
The mother doesn't seem as interested as she should. She shifts around
and lays on them without noticing, and while she is curled around them,
she doesn't seem to be prodding them to nurse or bathing them. She
hasn't had another in several hours, and isn't acting upset, but her
stomach still feels full. She is just laying there and purring.
I have tried to feed the kittens with a little syringe and cat milk.
They are eager to eat, but really don't seem to know how. One lapped a
little off the syringe.
Instinct tells me she is apathetic because she know they are going to
die, but is there anything I can do to improve their chances?
Also, even if we lose the kittens, I want to make sure the mother is
okay. She is the sibling of two of our indoor rescues, and I have been
trying to befriend her for two years. After I was able to sneakily pet
her once, she caught on, and has been sweet ever since. Are there any
warning signs I should look for?

Thanks in advance,
Mjoann