My younger brother’s disturbing behaviour - need sisters' advice

As-salamu alaykum sisters, I’m using a throwaway because I wouldn’t share this on my main, but I really need advice from other Muslim sisters. I’m 20 and still live at home. My younger brother is 15, and over the last few months his behaviour toward me has become strange and uncomfortable. It began when I found my bed covered in my underwear, neatly sorted by colour. I asked my mother if she’d done it; she said no and thought it was me. I confronted my brother and he just laughed, saying it was a joke. I didn’t see the humour and felt violated in my own room. A few weeks later I was sitting on the sofa barefoot watching a film with my feet dangling. I had painted toenails. Suddenly he came out of nowhere, grabbed both my feet, took photos and ran off. I chased him, caught him and made him delete the photos in front of me, but later I learned he’d recovered them and shared them in a group chat with his friends, captioning them in a sexual way. One friend even made a comment that made me feel physically sick. After that he swapped my hand sanitizer for nail polish remover so it burned my skin when I used it. He laughed when I confronted him and said I should’ve checked. He’s also been writing weird and inappropriate things on my mirror with a marker. I scrubbed it off but it left me shaken. My parents don’t seem to take it seriously - they tell him to stop and then move on until it happens again. They think it’s just silly teenage behaviour. He doesn’t act like this around others; outside he’s shy and quiet. With me he’s bold, disrespectful and careless. I’m starting to feel unsafe even in my own room. I don’t want to wrongly accuse him, but I can’t ignore what feels wrong. Is this something normal for teenage boys, or should I be more worried? How can I protect myself and get my parents to understand without making the situation worse? I’d appreciate practical advice on boundaries, safety steps at home, and how to involve the right people (trusted family members, an imam, or professional help) while keeping things within our Islamic values. Please: only reply if you are a Muslim woman. I do not want messages from non-mahrams.