When you are done with the 10 conventional mortgages…even at number 6 it gets onerous to keep enough reserves and to jump through the hoops for regular mortgages.  

Dining chairs for 6 when you sleep 10... 

In-unit definitely trumps in-complex because they often want to toss their scrubs in the washer when they get home and let it run while they sleep.

@Basit Siddiqi More difficult than regular books for accounting? 

Should I continue to reach out regularly in different ways (email, phone, knock on their door, etc.), leave them alone, refer to someone else or other? 

So the lender can use $1,500 of House 1's income to offset the $1,900 House 1 payment meaning your regular income needs to be able to cover the payment on that $1900-1500=$400/mo plus the cost of the new mortgage for house 2 AND since you mentioned you owned a duplex, you need to calculate the same income and expense calculations we did above to figure out how much you qualify for in terms of a mortgage.

And the returns are still excellent.2) In the right markets, short term rents allow you to earn far greater profits than regular long term rentals. 3) You can find ways to get discounts even in areas that are great returns.

@Jace Perez look at joining a wholesale or a regular real estate team. 

You could also try partnering with a private lender/investor that's willing to sponsor the deal - but be mindful that investors are already wary of buying co-ops as the main purpose of co-ops is to discourage landlords/investing and instead allow homeownership to regular folks. 

Host open houses for every listing regularly and make them fun.