This allows him to maintain control over all sides of the deal, from beginning to end while staying on time and on budget.

This will allow you to get the sheriff involved immediately.If you are already past the notice period then you will probably have to follow whatever state laws are in place for the notification period and possibly the eviction process.

I think one of the older resorts that still do allow short-term (Airbnb rentals) would fit the bill.

I either jack and jill the bathroom or add a hallway blocking off the bedroom portion to that bath to allow access for the rest of the members.  

Home prices in OKC remain affordable compared to national averages, allowing investors to acquire properties with strong cash flow potential.

that will not cash flow - you won't be generating "cash flow" from the property that will go beyond servicing the debt and allow you to pay down any principal. 

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

This is the best way to get good at analyzing deals and will allow you to quickly have a good idea about how a deal will work.

Currently I'm looking for some kind of methodology, software or app, that I can use to manage the properties, which will allow for another family member to step in to my role relatively seamlessly if I were to pass in the future.

My memory is that there was a time when we were not allowed to require them, but maybe I'm wrong or maybe the law changed back.