How do I get my step dads Daughter with her 3 kids out? Shes mean to my mom and it just doesnt work?

My situation is this, I have been living with my mom and step dad for 10 years since I was very little, everything has been great. Up to the point where one of his daughter's who needless to say is lazy and dependent on her fathers money has 3 kids. She recently left her husband, and moved in. Now, she just munches off everything, doesn't care about working, is rude to my mom, and over all is just messing up the relationship of both my mom and step dad who were doing really good. What do I do?