They both are low income and have a hard time making ends meet (paying me).

With my 50th birthday approaching I've decided to take it to the next level and hit it hard even in these weird economic times. 

Well most likely build but aren’t opposed to buying (inventory is so low in our area however).  

The main characteristics were that the exterior walls were constructed all at once with the same stud running from foundation to roof and the floors or levels were hung off of a cleat that ran around the structure cut into the vertical stud.

1st off- Kudos for your enthusiasm to tackle a difficult problem; adopting new materials and building science understanding on really old structures.Success levels for energy retrofitting will be directly tied to the level of "gutting" you do to the old house, especially trying to add a vapor design and passive ventilation retrofit. 

If you find better ROI, the chances of appreciation, which is where real wealth and freedom happen, is very low. 

There is always a way to find the "low hanging fruit" you just need to know where to look and work with the right people!

we eventually refied after only 9 months with a significant noi increase through fannie becoming cash on cash plus a sizeable non taxable event along with 5 years i/o at a very low rate which allows for a healthy cash flow

My wife and I work full time jobs, so dealing with tenants is a low priority. 

While there are low and no money down real estate investing methods you can explore, the reality is, you need to capital to invest in real estate.