Why don't you nicely explain to her that if she continues to neglect the babies the way she is doing, then they will die, which will make her child sad. Tell her that if you take the babies, they will live and grow up to be healthy and strong, and your cousin can play with them whenever he wants. Just remember that the only way to achieve something is to be nice and respectful. Don't tell her that she is bad or horrible, and don't argue with her. If you go about it the right way, I'm sure she will let you take them.