Any cat-rescue experts out there who can lend me some advice?

When we moved into this apartment back in October, I noticed a little family of kittens living underneath the laundry center; there were about five or six of them, all the sweetest, fluffiest little grey tabbies you can imagine.  Well, the kittens are now grown up (the ones who survived; I think there are three or maybe four of them left), and one of them has a new family of her own.  I don't know how many she started out with, but she had three last Friday, and near as I can tell now she only has two.  You know, a lot can happen to a feral cat living in a semi-urban area, and I would rather see the remaining kittens make it to adulthood.

We've been feeding (I think) the entire stray cat population of the complex in addition to our own two (indoor) cats.  One of the grey tabbies is imperious, and comes and stares in our front window until we bring her something to eat, whereupon she hisses at us and backs away, but doesn't run.  And when we put the food down she runs up and eats whether we stay there or not.  Her brother is a bit daft and much more shy, and Mother cat is clearly terrified of anything on two legs, and won't stick around if you even look at her.

She and her family are living underneath the deck by the swimming pool (and I hope that third kitten didn't meet a watery doom), and I have been taking food over to them, but although the kittens are willing to eat while I'm watching, as long as I sit far away and make no sudden moves, like I said, Mother cat won't even come out of hiding.

So what do I do?  The kittens don't look particularly healthy, although they are cute (well, they can't help that!).  The bolder one has a great deal of mucus oozing out of his eyes, and the shyer one with the white feet also looks a bit crusty about the face.  Kittens don't need to live in constant fear and hunger and discomfort, harassed by fleas and other insects, suffering from some kind of infection from the day they're born.  Kittens need to have a warm, comfortable home where they can eat all they like and grow up safe and loved.  I'm not sure how to catch these kittens, and I don't want to leave Mother behind to mourn the loss of her young and eventually have more kittens that need to be rescued in the same way.  We also can't particularly afford to adopt every stray kitten we find, much as I would love to do so.  And I don't particularly trust animal control not to shove them in some dank horrible cage for two weeks and then put them down when they don't get adopted.

Advice?