Most/all state governments have websites with exactly this information.  

You have to register with code enforcement, include an addendum in your lease that has something to do with criminal activity on your property (I didn't read it and didn't make my tenant sign it), and sign a clause stating you will allow code enforcement, or as I like to call them government agents, come onto the property to look for code violations AND inspect the inside of the house if they desire.

The state's workers compensation laws will govern ultimately. 

As I was reading your story I was getting ready for the tenant from hell story where they lived there for a year before you got them evicted, they trashed the place, and you never got any rent and were sued, and turned in to every government agency about code violations they did to your property. 

Does the government provide financial assistance to rehabbers who want to make homes wheelchair accessible or to the disabled in general?

Only a government municipality or IRS can. 

Perhaps I can find work with the government...                

However, my father, 85, receives a decent government pension of around $50k a year.

And even bigger and you may get sued, you may get scrutinized by government and so on.You make it to the next level by getting over those hurdles.

It's a comedy show which illustrates how to not run a family owned real estate development company.Almost everyone in the family can't stand each other, and the rest of the time their company is under investigation by the government for "slight treason charges".