July 26th I got a text from the tenant from a new number with another sob story wanting to stay, but still not offering a July rent payment. 

Will a DSCR lender give me a home equity loan from my (1st SFH) rental property, so that I can cover the down payment + closing costs to assume the 2.75% interest rate on a (3rd SFH) property I would move into immediately?

Don't stop making your payments.

Any thoughts how to avoid these types of situation like reverse rental payment?

The only way to avoid the simultaneous closing is if he receives the certificate of non-withholding. 

- $500,000 Purchase Price- $0 Down Payment- 4% Interest- 30 Year Am- 10 Year Balloon- Monthly payment: $2,387Business Plan: Convert to 44-pad tiny home (tenant-owned) community that will cash flow ~$20,000/mo and be worth ~$3.5 million!

We own a primary residence and plan to stay here (house hacking is not for us), and have been saving scrupulously for the down payment of our first investment property, ideally a 2-4 unit multifamily. 

I moved in with my fiancé and have renters in my house, and trying to get a heloc for a down payment to get to a second rental investment.  

A non-owner occupied loan is what you sound like you need.

We ended up with a lender that specializes in tiny houses out in Utah, but they ripped my arm and leg off in terms of interest rate and down payment.