Thank you for taking care of mum and wanting to help the family!
One thing you need to know: if you go looking for the nest and do not take mom and the kittens at the time you find it, mom will very likely move the nest. It's really a tough call what to do. Unless you can see where she's got the kittens without having to go near it, you have a tough decision to make. If you trap mom, and the kittens are in the nest - great. But if you trap mom, and she's moved the kittens to a new nest that you don't know where it is - the kitties will die without mom.
If you wait for mom to start bringing the kittens around (which she will very likely do - especially as she's still coming by for food), you run the risk of losing any of the kittens to illness, or getting run over by a car or something. But she wouldn't be bringing them around for food for likely 3 - 4 weeks.
If you're able to find out where the nest is without mom knowing it, the best plan would be to trap mom and immediately get the kittens. To do this, you need to have a room/space already set up for them. They would have to be kept separated from any of your existing pets - without a vet visit, there's no way to know what diseases and/or parasites they've got.
While mom will likely take care of the kittens just fine in the room you set up for her in your home, a great info site is http://www.kitten-rescue.com/
The kitties can be spayed/neutered as young as 7 weeks old, though many vets won't do it. But they really ought to be spayed/neutered before being adopted out. I'd wait at least until the kittens are completely weaned before taking mom to be spayed. Ideally, they should stay with her for 12 weeks before being adopted out - but realistically it's easier to adopt them out while they're 8 - 10 weeks old - at the mind-bogglingly cute stage, lol!
But letting mom do all the work - feeding, cleaning and training them - is definitely easiest! Whether that's in your home (the safest) or while you care for them while they're still outside is something only you can determine.
A list of great resources that will be helpful to you is in this thread:http://www.thecatsite.com/forums/showthread.php?t=16045
And most importantly - please feel free to ask ANY questions! And please keep us posted!