Some vets will spay your cat whenever, however many do not advise (and wont do it) until your cats milk has dried up. The milk will normally dry up about a week after mum and kittens are seperated. There was a reason for this, but I don't remember what it was.

Once your kittens are eating solids most of them time (prob about 6 weeks) you can stop them feeding from mum, there are several ways you can do this without actually seperating them, such as bandaging mum or putting the kittens in a cage, so they can see each other but not feed. (This is what my vet advised me to do with mine).

If you are in no hurry, you should just wait until the kittens have gone to their new homes. As I am keeping one of my kittens, the vet said I was best to seperate them for a bit as some kittens continue to feed for quite a long time after eating solids (i think it is a comfort thing), also my mum cat is very small and needs to put some weght on and I think the kittens feeding from her is really draining her alot.

Oh gosh, I just had a look at the pics, they are sooooo lovely! Well done mum!!! The look tabby to me, but I am no expert so I may be corrected.