----I do have a 'rental' in Joshua Tree House....

@Jose Almonte  In the multiple states, where we have rental houses, the tenants pay for all utilities, shovel the snow, mow the lawns, and take care of minor maintenace. 

We've come to realize that the Boston market is too tough and the numbers don't make sense (to even house hack), so just recently, we decided to hone in on Plymouth, MA... with the idea that it could be a good tertiary market to do furnished rentals (thinking short-term/AirBnB in the summer, and mid-term in the offseasons).

If one or two in 1000 houses would be open to a "cash offer" in the next 12 months, that means you have to market to them and the other 998 consistently for 12 months.

Me and my wife are planning to purchase her mom's house. 

We build houses; rehab houses; love our neighbors; and wouldn't think of living anywhere else. 

For a $100k house, we can agree on payment terms and pay the seller $120k over time.

Yes, the spring/summer season sees demand ramp up, but that doesn't mean a house listed in December won't sell.If you buy in October/November, chances are you won't be listing until January, anyways.If I had a house completed on, say, December 15th, I would likely sit on it through the holiday season before taking it to market, but I would talk to realtors.  

On one lot, he has his house.

I would encourage you to do the following to set yourself up for success -1.