Have you looked at what all the other houses on this street and in this particular neighborhood have?

100% financing is tough...even for private lenders, unless there are compensating factors (great track record, proven successes, strong reserves, great credit score...maybe even good job/w2 income (usually not a factor for non-bank investment property lenders, but may be for a private individual)). 

He has PCS orders and they are moving out at end of July.Couple downstairs with dog is non-committal about their plans, have given no notice, but MIL guy has suggested they are looking for a place and may move before or by end of one-year lease in mid-September.MIL guy has explained that he and his wife live upstairs and maintain that and the front yard, and the other couple with the dog live downstairs and maintain that and the back yard.

etc..You can try to go conventional, to a community bank/portfolio lender, or to a non-bank lender for the above. 

I’m not particularly worried about them, they always pay on time and I’ve never had any major issues with them.

I don't know whether this is typical, but my experience is based on several years buying foreclosures, and my wife as a VP for a finance company with non performing loans, many of which were real estate.First, for the foreclosures I looked at, most if not all were at public auctions.

Most private lenders, hard money lenders, and non-bank lenders will want to be the first and only lien on the property, so it may not be possible to borrow $50K and put a second lien/further debt on it.Why wouldn't you just finance the whole thing with one lender? 

I have been consuming all the great info from biggerpockets for 18months now but this is my very first post and I am excited to get insights, suggestions and particularly legal advice for my situation.I recently got laid off from a company that I had been with for 6.5yrs (since right out of college) and then within a month, they offered me another role which is outside US so I am very excited about the change and new experience.

Drafting and revising so many loi's, binding and non-binding loi's, poc's and several different other documents. 

The seller bought low and is selling high at your expense.Walk away, particularly in a high crime area.