You can win.. but for me.. it was put 160k in cash into escrow pay another 20k over 2.5 years and we finally won.. but even then she would not sign took another court order written exactly right for the title company to insure then the title company wanted 90 day period after the judges order etc etc.. so long drawn out and expensive.. so normally this is simply a sale fail.. in my case I had given the lady 50k to pay her back tax's so if i did not sue i would have been out 50k..  

Being able to get in and out is pretty basic safety issue I wouldn't like to be in front of a judge in MA on this, especially with the previous issue. 

Is there a way to declare myself a dealer or does the IRS make that decision?

I would leave that decision up to a judge after the tenant files suit and we appear in court.

How will the bank look at my income and judge my DTI?

As for the big claim of rent abatement, the judge will likely disregard it.

If you are only screening tenants as good as a property manager is(meaning only on paper), then thats not good enough, it needs a personal touch. you can judge them on everything that is not a protected class, so why not judged them on what type of job they have, how they dress, what kind of car they drive, how they discipline their kids, their mannerisms etc. 

How will the bank look at my income and judge my DTI?

Assuming your brother went to court and told them he couldn't pay due to the shut down, I can't see any judge evicting a disabled veteran.

(With the 1031 exchange you will not have any cash from the sale and at least as much debt.)If so, they’ll just declare it on their taxes and pay the appropriate rate depending on their income level.