CC, you're a good person for taking the feline family into your home and helping them out.
If you find that you are unable to care for them, however, I would strongly recommend contacting SMAWL, PAWS, ARF, or Friends of Felines before taking them to the animal shelter (where they are almost certain to get a death sentence...especially this time of year).
8 weeks is the "legal" amount of time before you can separate a kitten or puppy from its mother. Most rescue groups or shelters will probably not be allowed to take the kittens without the mother cat before then.
Also, you won't be able to have momma-cat spayed while she's still nursing the kittens; but if you want to get it done on the cheap, you should call the Well Pet Clinic (in Lexington Park) and set up an appointment for a few weeks from now.
I've just taken in my seventh stray; elsewise I'd offer to to relieve you of the burden...but my husband is starting to compare me with the crazy cat-hoarding lady they just found in Virginia.
Good luck with everything.