How to handle my boyfriends mom

She recently moved in with us due to her parents moving to a different Country. His mom has been diagnosed with Paranoid Schizophrenia a while ago. She doesn't listen and will leave the apartment with no key to walk around and talk to guys in the complex leavin the door unlocked. Right now I've been having to buy groceries for 3 people and handle the bills since they're in my name. I'm really stressed out feeling like I'm mothering a grown woman and feel like her parents threw her onto us even though she didn't raise my boyfriend. I feel like my standards keep getting lowered everyday, and I'm truly done feeling the way I do. Idk how to handle her or what to do