They wouldn't be able to get a mortgage, but would have to do some kind of SBA loan or other commercial loan for the business with the properties as part of the business.

I see that kind of structure (maybe different splits or thresholds) with first time LPs - it's generally simpler and easier to understand.

There are actually THREE kinds of subject to transactions1- subject to existing mortgage without lender approval2- subject to existing mortgage WITH lender approval3- subject to existing mortgage as part of a seller financed wrap around mortgage.with #1 and #3 it’s in everyone’s interest to utilize a third party servicer, who collects and then distributes payments.  

Some places do this annually, some places do a portion of the town every year giving them a total cycle of about every 4 years, and in my area it’s common to do a whole town reevaluation every 4-5 years.

What kind of system is this? 

Based on my previous investing history (completely unrelated to real estate), I would describe myself as a buy-and-hold kind of guy.

If they replicate that kind of profit reliably, what would they need you for? 

You're facing a common investor challenge: learning from experience (and sometimes mistakes).

You will need to put some kind of down payment upfront.

Kind of like a cash for keyshttps://martinezlawcenter.com/new-rental-laws-in-california-...Most of the long time investors I know haven't had problems but if you get a "professional tenant" in look out and call your RE attorney.