When to do it?

I have two cats. One delivered a litter of four 6 weeks ago and the other had two stillborn 2 weeks ago. When should I have them spayed?
I also have three feral cats with about 10 kittens between them in the woods around my house. Their kittens are about the same size as our six week olds. When can I take them away from their moms to get them good homes?

recomended time to give them away is probly 8-12 weeks old.. as for spayed, the vets here wont do it till they are a sertain wieght so i dont know on that one.