We run into this situation from time to time, but unfortunately, there isn't much you can do. In Virginia as of Wednesday (7/1/20), Marijuana will be decriminalized. Recreational use is hardly on the radar of police in our area and I'm sure it's similar in yours due to the aforementioned changes that are taking place.
With that being said, here's what I would recommend.
Do exactly what the lease states... It is your lawful contract.
Continue with the eviction on the defaulted unit as that's really the only way you can forcibly remove them. You could try to offer 'Cash for Keys', but at this point, they may have read the multiple headlines telling them they do not have to pay rent due to COVID... Yay
As for the lower unit that is affected by their smoking, I'd encourage you to explain to them what you are doing and offer them suggestions to curb the issue until you are able to remove the upper unit. One of which would be carbon pleated air filters. We have had success with either offering these to a tenant or getting them to purchase their own to remedy the smell as the carbon media captures the odor.
An alternative option that we use is to allow them to vacate, but require them to continue paying the rent and utilities. They must move-out and leave the apartment in rent-ready condition, we then market the property and hold them responsible until it is rented again. This is a compromise that works out for both parties.
Best of luck to you in July, Virginia has not been kind to landlords during this period of time.