I feel sorry for the two year old. If there is fighting and yelling in her environment it can severely affect her for life.

Your son should talk to child services, he should start recording this woman's behaviors. And I would be worried if this woman was out all night and your son leaves his child home with her while he works. Bet she leaves that child unattended while she sleeps off her boozing/drugging from the night before. That's not good and yet that's what drug addicts do.