UPDATE: I agree with @Anonymous and I think these guests are harmless enough inside the home, no matter what they are up to outside of it, so I took that bull by the horns, and asked what goes on with all the comings and goings. From that conversation, came the following note that I will send via Airbnb. I wanted to share because I don't think it is on the up and up and there is more to the story. If I do learn more, I will share in case anyone is interested.
Dear Guest:
To confirm our conversation yesterday, you let me know that the numerous (10+) and brief (2-15 minutes) trips in and out of the apartment each day, both with and without Alex, are to vape and use edibles away from the apartment. As I explained, this activity has caught the attention of a couple of neighbors. I don’t think they have said anything to the apartment manager, though the manager does live within the three buildings that share this parking lot.
Even though marijuana is now legal, please remember that this is a shared community and the neighbors need to feel comfortable. I am fortunate to live in a good community, and one of the better parts of the complex, and I want to keep in good standing with the management and my neighbors. With this in mind, if you can reduce how often you come and go for brief stints, both to the parking lot and driving in and out, that would be appreciated.