Unfortunately Missouri has no laws for renters. It sucks. We were in a similar situation with awful neighbors but also had water damage in our apartment that became moldy. We also lived without hot water for 2 months. There was nothing we could do. I was so glad to get out of there and we had to pay to break our lease. Then they took over 2 months to process our move out. Still nothing we could do.

I would suggest getting a carbon filter for your furnace/ac. It helped a bit for the smoke smell in my case. We also ran an air purifier with carbon filters in those rooms that smelled strongly.

Edit: for spelling