Doesn't your heart just break into tiny pieces when you see a momma trying to look after her babies outside like that all alone, i really feel for you in your situation, alas we cannot save them all, and if only humans were more responsible and all loving and kind as you are, we would not have this problem, but in the real world it is sad to say we have many beautiful animals out there needing love and care.

Just try and do the best you can,if you know going to the shelter will end up in them be putting to sleep, i am not sure that is the right option, but then you don't want them suffering either out there, such a hard call,i will be thinking of you and hoping you can find a way to help these poor babies, love and hugs.