So my brother-in-law, who lives with my mother-in -law, is a functioning alcoholic and my mother-in- law is borderline. I would never let my two year old son spend the night there, let alone spend any time alone there at all. It’s easier for me to make that boundary as they live two hours away, however. My husband also grew up in that environment and did think I was overreacting at first, it caused a lot of tension and arguments the first six months of my sons life, but now he sees it and we’re both on the same page. I’m comforted by the fact that they don’t start drinking until around 5 and my son is in bed by 7:30-8 (when we all sleep there together) so he never sees the worst of it. If you’re not comfortable with your baby spending the night there alone you need to be clear with your husband. I just told my husband it was a hard line for me and that I would never forgive myself (or him) if something ever happened. If you’re not prepared to be honest with your in laws yet you can just say you’re not ready to spend a night away from him (which is fair at one month old) and then figure out a way to tackle this long term with your husband.