My sister is in her room with a guy?

I'm 14 but my sisters 16 she brings her boyfriend into her room like 3 times a week when my moms not home.her boyfriend is like 17 but so skinny.I'm 14 and I go to la fitness daily I am very active and fit and I lift 240lbs.I'm very strong and I'm 5.9...she nos not to bring boys home.and her bf frustrates me and constantly pushes me around.so she I take action and kick his as* or leave it someone answer