Stepdad is favoring stepbrother over my other stepbrother.. help?

my stepdad is really favoring my stepbrother over his older brother... i see it happening and its really really wrong. my youngest stepbrother is BAD. he just finished grade 8 and hes doing drugs, drinking and bullying kids like crazy and my stepdad keeps catching him doing it but doesnt even punish him.. then my other stepbrother (who is 16) is like really good and really shy, my stepdad is constantly talking down to him and making him feel horrible about him self its crushing his confidence even more.. and they're mom died a few years ago so i feel so horrible for him, hes never home because he scared of being bullied by his dad.. I know hes gunna resent his dad forever after this.i really want it to stop but dont know what to do. has anyone faced something like this before? and any ideas on what i can do? any answers are appreciated thanks!