If the wall is severely compromised and cannot be treated, replacement would likely be the best choice to ensure the health of your tenants.As for future prevention, the dehumidifier plus increased ventilation is a good idea.

Under no circumstances should you do anything to the tree that will damage its health or remove it without the explicit consent of your neighbor.

Are you able to change batteries on technology like Ring devices, Smart Locks,smoke detectors, etc.?

Will it be enough to cover health insurance.

We both are nurses and will be working in the Atrium Health system. 

Personal risks of your health, becoming incapacitated or injured and again insurance aspects.

I have friend who is renting a house in Minnesota who is a wheelchair bound 100% disabled veteran with documented and on going mental health issues.

There's no health insurance or other corporate benefits either.

Houston led the nation in job growth in 2018 creating 120,000 jobs and is expected to do so again in 2019 with health care, construction and administrative services providing the strongest performances.

Your tenants have raised a reasonable health concern.