If you're looking for basic income/expense tracking, I'd suggest checking out Stessa.

Most lenders but not all, should use the existing 2nd unit lease at 75% of gross for extra income to qualify on either loan types.

If you don't have patience or expertise or time I would just sell and 1031 exchange into a property that generates income, appreciates and helps build wealth.

My accountants won't even touch them because its not economical for them (even if billing by the hour) nor their clients.If you want the kid's Roth to grow, consider how to generate earned income for them. 

Currently have a couple rentals, a flip going on and made income from 2 different LLC last year.

By selling all units to us, he didnt need to do that, and because he's financing he will earn money over 5 years like he hoped.

Passive income is money that you earn without actively working for it.

Really and how will he do this with zero income, and only 50k ? 

I have a 9 to 5 which I plan on keeping, so all money earned from cash flow will be reinvested and saved to be used on the next property.

That would eliminate my current ~$1100 monthly cost of living renting and pay for the house itself with rental income