I'm going to tell my parents about my suicidal stepsister
Is she really suicidal? Why else would you do this?
I'm tired of hearing their nagging about my life. They are always blaming me for everything and praising my stepsister
Even though you have a terrible reason to tell on your stepsister, it is good to tell your parents about your suicidal sister. She has a very serious problem and she needs help.
I doubt she really needs help again.
Well as long as she is safe I think that's what really sounds. You can be angry with her later but death is permanent. You are doing the right thing.