Fear for siblings' welfare

Hello,
I left home 2 years ago to live on my own as life was becoming unbearable with mom & stepdad constantly fighting, violently even, break-ups every couple of weeks, & mom's constant drinking & moodswings. My brother & sister are under 18 & still living there. I'm worried that kind of life will harm them emotionally & physically, especially my brother who is 15 & very sensitive. They seem happy sometimes & I see then rarely, but what are warning signs that perhaps they have taken to drugs or are experiencing mental distress? I am afraid that will happen & I'd like to be able to do something before they get to that stage. What can I do?

Thank you

Would it be possible for you to care about them more often and take them away from their home now and then? That could make a big difference.