About a month ago, I had a new tenant move into the upstairs unit of my property.  Almost immediately the tenant in the basement started complaining about noise from thier unpacking, her cat and dog making noises, and marijuana smoke (which she has for medical purposes). I would reach out to the upstairs tenant about these issues and they assured me that they would only smoke outside and that they took steps to mitigate the noise in an effort to be as respectful to the tenant downstairs. 

However, I still received complaints from the tenants downstairs about smelling weed and that their asthmatic kid was having trouble breathing. When I would reach out to the upstairs tenant they would give a completely different story about how they are doing something mundane or not even be home at all. When I got a complaint from the downstairs tenant at around midnight about how they couldn't take it anymore and that they were leaving for the night because of the smell, I decided to visit this tenant and see if it smelled like weed. When I went into the tenant's apartment I discovered that it didn't smell anything like weed or a strong smell of fragrances or air freshener that one might use if they are trying to hide the smell.

Since I didn't smell anything and the tenant downstairs isn't happy I offered to allow them to break the lease and find somewhere else to live where they could be much more comfortable. They agreed that they would take this option and look around for a new place. A week after this agreement was made they called me telling me that they wanted to call the police on this tenant because of the smoke. I called the tenant upstairs and questioned them about it they were confused because they were just cooking dinner. I told the tenant to call the police because if they feel that the tenant is actually smoking weed and lying to me. The tenant then came back to me saying the police advised them to go to the courthouse and file charges but, not charges I guess (Idk what this part means) towards them and myself because they are my tenant. The downstairs tenant said that they have messages (probably from very early on) that they didn't realize the weed smell was significant. I asked for a screenshot and they just replied "the tenant upstairs has screenshots of the convo as well."

On the other hand, the tenant upstair feels like they are being harassed with the constant complaints towards them, every time they shower they hear the toilet flush which makes their shower scolding hot. They have also overheard the tenant below plotting with people on the phone about how they will get the tenant upstairs out and that they will sue me if I don't make this right. Lastly, I have heard from the tenants that have been there the longest that the tenant downstairs complains about everything and is untrustworthy as well.

I'm kinda at loss on what to do here, any advice on what I can do moving forward from here?

THIS IS IN BALTIMORE COUNTY