I am 21 and my cousin(18) is misbehaving with me

my cousin (18, chacha's son) is staying in our home till he completes his college. my family sleeps in same room with separate bed (for parents and me and sister) We thought of giving the separate room for cousin, but he was kinda afraid so we allowed him to sleep in our room in his separate bed. After somedays, he came near me and put his hand on my chest. I always wrap myself with blanket even in summer. He just took my blanket and placed his hand on my breast. I immediately thrown his hand away. He thought I was sleeping. I pretended as sleeping and he continued the same with me. He placed his hand on my little sister(15) thigh's. I know some people out there still blame the victim for dressing. I never wear any shorts or tshirts. I dont wear tight clothings to reveal my body physique. I don't have much physique. I am scared now. I think even if i wear burqa nothing going to change their minds. Many years ago i got news from another cousins that he was watching adult content in his phone and he was ignorant to delete in his browsing history. At that time i didn’t care. Even now I don't care whatever he watch in his phone but why he is trying those with me and my sister. We are treating him as brother. Also he has a sister in his house. will he do the same with his own sister? Idk whom to inform? should i tell my parents or his parents or should i tell him ?