@Krishna Chava Thank you for your response I agree with you about most landlords but I am referring to more serious mold problems where all the dry wall needs to be removed and replaced in a room or two. 

You run the risk of losing them as tenants -- Consider, if they leave -- how easily and quickly can you replace them with market rate tenants?

An structural engineer will probably cost around $500.

In addition to Sheetrock replacement, usually....ac handler, many electrical components, many plumbing components, etc.  

If you don't have an urgent need to replace them now then I would move them back towards the end of your rehab cycle to see if that changes.

My goal is acquire rental income to replace my own income eventually.

I have an opportunity to invest 70k in a franchise that I can scale into a business that would more than replace my salary (low six figures).

They stabilized the chimney with 2 jacks, gave a lifetime warranty, and engineers approval. 

I also had to get the HVAC replaced in its entirety.

In the 12 months, we fixed the landscaping, ripped out the subfloor, replaced it and carpeted, ripped out the hot tub and sauna.