Make sure whatever bank you approach isn't a big chain bank.

Any ideas how one can approach these owners? 

You won't likely find a master list of every way to process homeowner lists to find motivated sellers, but know that people build their businesses by doing just that kind of analysis on a recurring basis, always looking for a new way to approach marketing.

I had not thought of the "test advertisement" approach to get an idea of interest in the market, great idea!

I'm  preparing to approach them that I'd like to learn about the business, as my mom does most of the managing (reluctantly) than my dad the investor/handyman does.

What you need depends on how you choose to approach the business, how you plan to find your deals to wholesale.  

Best approach to finding them is through bigger pockets or local meet ups!

I have an area and investment strategy in mind but when I went to get pre-approval for a loan I hit a wall - the local lender I approached told me that my DTI is too high.

I've got some properties that are FSBO but I'm not entirely sure HOW to approach the seller.. 

I suggest that you approach a few small local banks.