I would most definitely check on the property first.

Have they ever paid rent with a check? 

I would just follow David Greene's method in his book on the topic: https://www.amazon.com/Buy-Rehab-Rent-Refinance-Repeat/dp/B0...Or could you check out my video on the topic which in my biased opinion is pretty good: 

I will check them out

Check in with @Joseph Chiofalo for Pro Forma support and analysis he can help plug in loan terms with investor friendly financing. 

Please include:When and how is rent to be paidWhen and how are utilities going to be paid (if any)When and how is the cleaning going to be (if shared or provided)What are the costs associated with damages / breaking stuff / calling a technicianWhat are the costs of breaking the lease, finding a replacement if you are doing short term leases on the roomsIf they lost their keys or check bounces what is the charge for it, how the cleaning of the common areas is going to work, and enforcing quiet hours.

I see these four rentals providing us a regular stream of income during retirement. 

You can also check meetup.com or search Facebook for real estate investment groups, clubs, or meetings in your area.You will learn faster if you rub elbows with people that have been there and done that.

Please check my numbers and let me know how we did and maybe what specifically is good, bad, and potentially concerning.

Tough to beat this answer from @Michael PlaksYou can also check out these two recent posts that walk through Section 121 Exclusion and 1031 Exchange guidelines and strategyHow Section 121 Exclusion and 1031 Exchange works: https://www.biggerpockets.com/forums/51/topics/1195208-1031-and-sec-121-experts-want-to-sell-rental-but-tax-worried What not to do if you don't meet the requirements for Section 121 Exclusion and 1031 Exchange:  https://www.biggerpockets.com/forums/51/topics/1195383-5k-for-cap-gains-tax-opinion-quote-that-reasonable ...