Living with crazy family

So my husband, our son and myself had to move back in with his mom almost two years ago, he didn't have a great job (which now he does). There's been battles since moving back in since she's an alcoholic and we have different view on life in general. It's been a challenge but tolerable.

About 5 months ago his sister moved back in with her THREE kids!! This is a small 3 bedroom house so she's sleeping on the couch my husband and I took the small room so the kids had more space and now everything is crammed into a small space. We're trying to save to move but his mom just raised our rent so now we have to adapt to that and we're trying to fix our credit.

We recently found out we were expecting, and there's no way I'm bring another child into this house.... I need advice on how to dig us out of this hole.... I've already told my husband that if I have to leave and be on my own I will cause having another kid here is not an option.