Help?! Cats and Kittens?

I rescued a cat 2 years ago. He became my sister's cat but she's going to college so he's mine again. I rescued another male stray cat also about half a year ago. I rescued 2 more male kittens 2 weeks ago. Now my friend's outdoor cat had 4 babies and her dog ate one of them so she asked if I could "rescue" her cat and it's 3 remaining babies. Her parents won't let her bring the cat inside. It's also very rainy and we are afraid the babies and mom will get sick. I can't take them because we can hardly afford the cats and one dog I have now. None of my friends can take any more cats because most of them already have at least 2 or 3 because they adopt the cats I rescue. Nobody could take the 2 white ones so I kept them. After them my mom said if I sneak the pregnant cat into the house she'll get rid of the kittens and my precious rescue cat Shadow. I don't see why she loves my sister's overweight cat so much. Anyways, how am i going to help provide shelter for the cat and kittens? Maybe I could tell my mom I need them for further veterinary studies? I could pay for all of their expenses because I sell my artwork online and do multiple various tasks for neighbors and friends. I'm painting much more artwork now too because I have to pay for my 2 kittens to be neutered and etc because my mom said if she payed for them she would de-claw them like she de-clawed my sister's cat. I also promised my best friend that once she got a cat (one of the other cat's 3 babies) that I would help her pay for all expenses because she is poor and her mom wants it to not visit the vet or get fixed and she wants it to live off people food because she doesn't want to spend much money on it. I love cats too much to let that happen so I promised that I'd sell her artwork also and we'd use our artwork money to pay for it's food and vet expenses. Right now I just can't figure out how to shelter the cat with the babies, We do not want her dog to eat any more and we don't want them to die or anything. The only reason I couldn't sneak them into my house or whatever is because I don't know if they have feline leukemia or AIDs or worms or anything that my cats could catch and would be very expensive to treat or non-treatable at all. :( What can I do? Nobody can take her I have already asked everyone I know. Help?