I have done a fix n' flip, and have a short term vacation rental currently.

Short of risking tax evasion, you can either: (1) plan to pay the taxes twice; or (2) find some alternative method to do wholesale (e.g. option method). 

If you inspect 75 to 100 houses in your market (in a short time), you'll not only be an expert, you'll also find a great deal (you might not know it at the time, but you will stumble on one.)Best.

I'd love to give them a short-term out (we purchase the property from them by getting a mortgage after X months) and a long term option (say, 3 years).

Short answer, give a call to your contractor license board and explain what you want to do, it could be anonymous.

If you are looking for a place to invest disposable income and get a moderate return higher than that of the stock market the answer is probably yes.

I started with a couple stocks and now work full time and have a Roth IRA, Roth 401k and working on life insurance.

So for the short term, you need to keep enough funds to protect for any negative cash flow you may encounter up front.  

GroundBreaker - https://www.groundbreaker.co/ -Real Estate Fundraising and Investor Management Software PatchofLand - https://patchofland.com/ - matches accredited and institutional investors seeking high-yield, short-term, asset-collateralized investments to borrowers seeking more timely and consistent sources of funding for rehabbing properties across America.

As Dan said I would look into Airbnb depending on how short short-term is.