I would be more concerned about taking them in at that age if you had other cats/pets. Unless and until they're able to get fully screened and vaccinated, there is always some chance I suppose that they may have something other cats could contract. This would be special concern since the mom was a stray. In saying that, however, I'd note that I am not a vet; anybody who is or knows more about communicable disease among cats can correct me if I'm wrong.
Welcome to the wonderful world of cat ownership. They're amazing animals and companions.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher