Kitten information - scroll through the ages to see where your kittens land:www.kitten-rescue.com
It can be very difficult even for a vet to determine.
If you are going to adopt some of them, it's best to leave them with mom until at least 8 weeks. Just keep putting out food and water for them.
If you want to work on socializing them while they're still outside, the basic trick is to just let them get used to your presence. Do not try to approach them, do not try to reach out to them. Just get nearer and nearer to them over time.
If you want several of them for pets, you'll need to trap them and get them to a vet before you bring them inside.
It is safe to spay/neuter kittens as young as seven weeks old. Most vets, however, have no experience working on such small animals and won't do it. Our vet uses the baby teeth falling out as a guide - this usually happens at four months. But for the ferals that we are trapping, sterilizing and releasing, they'll spay and neuter them young.
If you decide to leave them outside and not try to get the others adopted out, you need to decide whether you are going to commit to this or not. If you are, continue feeding. But they all need to be trapped and sterilized so they can not propogate more homeless cats. This includes mom.
If you are not going to commit to this, then simply stop feeding them now. Better to let them learn how to hunt and to learn which garbage is "food" and which is not if they're going to be on their own.
If you are going to commit (even if it's to a few inside and the rest outside), you'll need to think of the outside cats as a feral colony, not as outdoor pets. They may end up becoming friendly, pet-like cats, but that takes time, and there's no guarantee they stick around. Unlike our indoor pets, if they need to see a vet (which happens - they get sick just like other cats), they'll most likely have to be trapped, vs. indoor cats which can just be picked up and put in a crate.
We always rescue the kittens and find homes for them (and we have them sterilized and vaccinated before adopting them out). It is easy enough to build a shelter for them in winter (they may not use it).
Please be aware that if you do anything that seems threatening to mom, she'll move the nest again. But if they're almost half the size of mom, it's probably time to bring the few inside that you want to keep as pets. Again - this is probably best done with a trap.
What you may want to do is put the food you're putting out into a crate, and let them get used to eating inside of something.
Trapping hints are here:http://www.thecatsite.com/forums/showthread.php?t=16045
If you want to find a shelter in your area that may help, use this link:http://www.pets911.com/organizations/organizations.php
Type in your zipcode and let your fingers do the walking! Even if you decide to keep some of the kittens, you can call these places to see if they know of low-cost spay/neuter services in your area, or if they have or know where you can borrow a trap.
You can also use the yellow pages to call around to local vets to see if they know of low-cost spay/neuter programs or have a trap you can borrow, or know of a shelter, organization or person that can help. All of the vets around here know to call us when they get a call like that!
If you decide to trap and adopt - whether it's adopt out or keep - go for it. You may have to foster a few you're planning to adopt out for a little while. But if you trap mom, just make sure you continue trapping until you've got all the kittens. In our experience, mom cats usually disappear after being released after being sterilized, so if the kittens aren't 12 weeks old, they won't have been fully prepared to care for themselves.
I think you're sweethearts for wanting to help these kittens! It's just that caring for cats - even if they're feral - is a commitment, and no matter what you decide, just make sure you think it all the way through first. It is much better to do nothing than to partially do something and then stop.
Of course, we'd love to help you find all the resources you need to get them all spayed and neutered, and to help you socialize kittens you decide to keep, and to help you get adopted out the kittens you decide not to keep. Just let us know what your questions are! TCS is a great resource.
All my best,