clairific

Ever since I moved in, I've seen stray kittens in the hood here and there.
I recently found out that there are 3 tiny kittens and a teenager mom cat (?), and they live in the piles of garbage in our backyard.
I've started going out there twice a day to give them kitten food, give them water, and talk to them. They're all really scared of humans, except for the black & white one who's pretty ballsy. They're all very disheveled and unhealthy looking, but still adorable.

Now, I'm going to continue feeding and befriending them, but I'm wondering what the right course of action is here. I can't afford to take them to the vet, maybe I should start taking up a collection to get them spayed/neutered and shots, and they can just be our outdoor kitties. Or maybe I should get a cardboard box and take them into SPCA? Or should I ask neighbors if they're theirs? Not really sure, I feel like I should act quickly before they become too feral, but it's just not affordable. Any ideas?