weird predicament with my mother

so i figured out my mom smokes weed and im not sure what i should do. im pretty sure my dad doesnt know so i dont know if i should tell him or not. should i confront my mother? im very against weed and i know my father is as well. she already has a serious alchohol problem. i feel like if i dont tell my dad it would be wrong. and im afaid it could case alot of tention in my house hold, even along the lines of a dvorce. please help i just dont know what to do and i know she smokes because i found and can straight up smell it through the house