Boundaries Help !

My friend Macy and her son Luca recently moved into my home . I knew before moving them in that he’s a very young child as we’ve been friends for years pre baby . My husband and I accommodated them as much as we could , with the understanding of how kids operate ( somewhat lol ) . Well little Luca is 3 nonverbal ( he talks just not often ) and lacks boundaries. I’m not surprised or upset by it , but would like to help . She does think that he is autistic if that helps any advice given .

Luca keeps opening doors to the bathroom and she doesn’t want him in there , but instead of telling him “No” she will pick him up and carry him away or something similar . It’s not working because he STILL tries to go into places she doesn’t want him .

He is now opening my desk drawers , going in it, and taking things . Instead of saying no , she’ll push the drawers closed and move him into the living room . Now I’ve come home and my desk is facing the wall to where the drawers aren’t accessible anymore. I can’t come home and use things as intended because they’ve been turned to the wall so he can’t touch them. What can we do to help Luca learn boundaries ?