One of the house I am going to offer on is built in 1957, well maintained and is a 3/1 house of 1400 sq ft.

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.

It's up to you on how much risk you want to absorb and for how long and come out positive. 

As a side note, the company was paying my living expense abroad, so really I was tripling my savings rate.I am not sure if the company you are speaking about is trying to get you to move for a new job or if it is your current employer needing your skills in a different location, but leveraging them to protect your position might be a better strategy. 

Your family member could also provide the financing on it and make money every month with a positive cash flow spread between the debt and the rent collected or be like a guarantee person that is the main backer for the long term loan your Bank or other lender that  owns that property with a long term loan with that property  on a security  loan until that loan is paid off.Not saying the fix up budget makes this decision fairly difficult but i would say to not have a house that needs over $5,000 on the "make ready" expense to make a 20% gross return giving a cost price and sales price you gave on your example.What you could do to find a deal is pretty limitless. 

The landlord shall at all times during the tenancy maintain the dwelling unit in a habitable condition.

It should be pretty simple with your employment position but I would look at the possibility of reducing my mortgage payment and try to save up 3 if not 6 months of paying all of your expenses and change your mindset and do not be a big spender any more and only take anymore debt that does not make you money.As far as new investments go I would look at possibility of taking a home equity loan. 

Is an LLC costly to maintain?

I would also be sure to get all of their contact info again to include emergency contacts etc. so you can maintain communications with new tenant.

When the next recession comes (they historically happen every 5-10 years and the last one was '08),  I'm not confident that the population growth will outweigh other negative macroeconomic factors...I strongly doubt we will see anything like the '07 crash, particularly because of the affordable housing shortage, labor shortage, lending reforms, and all the positive migration, but that doesn't mean we won't see a pullback.