How can i get custody of my 2 cousins?

I have to cousins, Josh who has epileptic seizures, and cody who has adhd. My aunt is bragging that there getting on SSI and that she will have all this extra money now and that her life will be made. Every day both the boys are at my house, except in the summer she ships them off to her sisters house. She sends them there so she doesnt have to see her kids. And her sisters house is so discusting, it is filled with dog crap and urine and they have to clean it. When they are out there they are treated like slaves, have to clean up after the dogs which there is like 8 dogs. They are also told to chop wood with an axe. This is not something they should be doing especially when they both are only 14 and 15 and both have a mental disability. This does not bother their mom one bit. She doesnt care what her kids are doing as long as she doesnt have to watch them herself. So since i live a few houses away from her, she wont let the kids stay with me for the summer because she wants to have the house to herself. This is highly cruel and just rediculous. Can someone help me with this problem? I would really appreciate it.