My 15-year-old daughter refuses to do anything around the house. She lies on the couch, watches TV, and eats. She also thinks that she doesn't have to do anything I say and has it in her head that she is the boss, and terrorizes and yells at her younger siblings. I am at my wits' end. Any advice?
If your daughter behaves like this now, my guess is that she has been terrorizing the family for a long while. In other words, she is out of control. I urge you to get professional help right away mainly for your own sanity and safety and that of your two younger children. You could start by calling the local child protection agency or the school and enrolling in any parenting classes they might offer, especially a class for parents of out-of-control teens.
You seem to need help in setting boundaries and consequences for your daughter that will really have an effect on her behavior. You need tough love. This is not very easy, but for the sake of everyone in the family, it is worth the effort and the time.