Is being angry for seeing your parents taken advantage of valid?

My parents pay for mostly all of my brothers living expenses including rent, car pymnt, car insurance, utilities, etc. & have custody of his child who is 4 (by order of the court). He is no good and his gf worse. Both have had drug problems and problems with breaking the law. They give and give to him and he takes and takes. Is my feeling hurt, cheated, alienated valid? I'm a good person, good family. I am his older sister. My parents have always overlooked his short comings and now I see him taking complete advantage of them and they lie to me to cover. What do I do how do I cope? They are senior citizens and even raising his child is taking a toll on their health. I no longer speak to my brother because he allowed his gf to hurt me and my daughter by making false allegations about us. This is hard.