Even if your relationship to the family member doesn't make you a disqualified person to their IRA, you may still run into trouble if there is any preferential treatment at all (i.e if they don't structure the loan identically to any other loan they would make, it still could result in a prohibited transaction.)

I recently closed two deals where I paid the sellers a net amount and I paid all the back taxes and closing costs.My question is, can the property taxes as well as the closing costs be expense'd at year of closing to ...

Sub S is terrible for capital gains treatment and flexibility in passive investing so very few use it to buy and hold.

I had to fix a few things, put in central air, and termite treatment.

You have laid out drastically different investment vehicles with different capital requirements, time horizons, risk (both systemic and asymmetric), returns, tax treatments, time requirements, debt availability... ectIt looks like you have a bit of shiny object syndrome. 

Inventory, or stock in trade, is specifically excluded from Section 1031 treatment.

This would not qualify for tax-deferred exchange treatment. 

Properties acquired with the intent to rehab/fix and then sell/flip to not qualify for 1031 Exchange treatment. 

(We are retired now due to his cancer).

Limited partnerships and LLCs typically used for these investments are pass-through entities, meaning the tax treatment flows through to the investor.