My mom caters to my little sister even though she has a drug problem and neglects her kids, what should i do?

your mom is an enabler. Your sis will never even try to get better because you mom supports her in her addictions.I am sure you heard of tough love.That's what mom needs to do before sis destroys her kids. Kids need security,it builds who they will become. If they are insecure they will act out,pick the wrong people to look up to. CPS would work,maybe one of you could take over her duties.Kick her to the curb and tell her she can never come back unless she is clean and sober.I have had friends like you sis. They even had their kids removed forever.When they tierd of doin dogs in a crack house for some show,and tierd of living under viaducts they went for help and did get clean.But they had to want it and they went threw hell to make that decision. Oh yea....I do have dead friends too. Sooner or later you will end up with those kids,do you want them before she destroys them or do you want to be there for the after affects of her!