I will be looking into the opportunity with a partner who has several years of experience in RE and good amount of client network.

Most conventional lenders will require at least a 6 month seasoning period.Are you sure you can get a Refinance loan amount that is 83% LTV?  

So my question is, do I go with my instincts and take the usual deposit or do I credit and background check the father?

I have a small handful of investors who lease blocks of apartments from me, pay me a fixed monthly amount, and they lease to STR. 

It's really a shame because I figure I'll need to double my loaned amount to quit my job and I couldn't sustain paying the existing loan off w/ my day job.

And only if the lender agrees to finance the amount...agrees the collateral is now worth 80k more than earlier purchase price.

But I’m willing to wager that with the same amount of effort and cash, you will be able to leverage the experience of professionals, to build something of your own that perfectly fits your financial goals, limits risk to you and your family, and is repeatable if you somehow lost it all just because you chose the “hard” route.

An assessor would tell you it was due to a large amount of water- most of the time not covered.  

If you have an IRA with sizable amount in it - there are many legitimate ways to invest while earning a handsome returns, you just need to consider little different approach. 

But we have her security deposit, can we not give her anything back and keep the security deposit for the month of July?