Portsmouth, known for its historic charm, offers higher prices but strong demand for both multifamily properties and short-term rentals, with premium rental rates for well-located properties.

I am looking for suggestions on how to structure a partnership (short term) that will benefit him but allow me to be dissolve our partnership after a couple years as he isn't interested in long term holds. 

If you do place the property in her name, then inherit it later, it does allow for you to receive a step up in basis at that point, allowing you to sell the house shortly after her death without paying capital gains tax.5. 

Depending on your current rate or if the current loan is short term or long term.

That is tight leverage for an investment 2nd position loan.A private investor might be willing to do it, it's not going to be cheap at all & will be short-term money & will not be a line of credit to take out at your liking.What is your rate on the 1st?

Long story short, his crew blasted through the job in a few hours and the clearance test failed.

If you find someone giving you confused looks, seek a mortgage broker that helps investors.I'm not so sure how they would calculate income from short-term rentals.  

Short term rentals in St Pete are technically illegal but it doesn’t stop hundreds of other investors from doing it.

Metro Atlanta, generally speaking, respective markets 30 to 45 minutes from the City, will be tight on cash flow unless you implement a creative investment strategy, such as short-term rentals, medium-term rentals, or rent-by-the-room properties, or allocate at least 30% to 35% towards your downpayment if you intend to hold the property as a long-term rental. 

My wife and I have done all the terms (short, mid, long term rentals) and have done some live in flips.