I would have an attorney familiar with real estate principles draw up the agreement. 

The example you provide in the OP is a perfect illustration of this principle. 

I'm honestly trying to be objective here.

In order to remove that contingency, they’d likely have to sell, pay realtor fees, find a rental, move, try to time out a lease, get accepted offer and move again.I would like to provide a “solution” by buying their house and renting it back to them for principle, interest, tax and insurance.

It allows us to aggressively pay down our principle with income and idle funds, while retaining full access to every dollar we deposit.

Remember as a Realtor your job is to make the deal happen, not be the Principle in the transaction.

My question is: should I switch to a 15-year fixed loan and put more money towards my mortgage on my current property so that I am paying more on the principle rather than interest or should I continue with the 30-year fixed rate so that although I'd pay more in the long run, I am paying a lower price each month, allowing me to save up to purchase a property to rent out and make a profit off that? 

My question is: should I switch to a 15-year fixed loan and put more money towards my mortgage on my current property so that I am paying more on the principle rather than interest or should I continue with the 30-year fixed rate so that although I'd pay more in the long run, I am paying a lower price each month, allowing me to save up to purchase a property to rent out and make a profit off that? 

But my understanding was that would only be the principle and interest not the full rental income. 

Certain principles apply to residential real estate as well.