J.T.
sounds like your mother is a bad mother. she is allowing your sister to live off of her and is not allowing your sister to become a responsable adult. where is the kids father? would they be better off with the father? its not about what you want or what your family wants but what is BEST for those kids.
you cannot make someone be a good parent. You already have a house full of kids and I am not sure what age they are but if you can help her with laundary and when they stay with you to give them baths. Start teaching them how to take there own showers too. They can clean themselves if your mom is willing to get them into the bathroom. Its time for the five year old to wash himself and the four year old might be able to start learning too.