1. Getting child support when you don't have custody of the child may be fraud. You need to send that money to whomever is raising your child
2. If your child was removed from your care, there is a reason for it. Solve the reason and you can get your child back.
3. If your child has been removed from your care by the state, there is no way the state will let you raise your sister's children. With sisters both losing custody of their children, there is some major problem here. You may need counseling to recognize it.