Find out what is most important to your partner - is it tax benefits, guaranteed return,  split of the profits...

I owe $70k on my mortgage and a balloon payment of $30k.

You should do something like this in cooperation with your accountant because you don't want to mess up your taxes and have to pay for something you shouldn't be paying for. 

The current rental income is $5,300/month, while our mortgage is $1,500/month, property tax is $600/month, property management costs $200/month, and maintenance expenses are currently unknown.We’ve utilized a HELOC from this property, amounting to $300,000, for renovating the basement and investing in a preconstruction condo and another property in a different city.

A couple of my favorites are Opportunity Zone Tax Credits and Low-Income Housing Tax Credit (LIHTC).

LLCS are sometimes important to the states who won't let you homestead (get a tax break) a property in an LLC. 

Offer to pay 100% of dues owed if they waive all late fees and see if they will forgive/reduce any legal fees. 

I have even had situations where I had to amend my taxes because the tax person screwed up.

Worst case scenario is they take 8% of your rent money and then at the end of the year you get to take that as a deduction on your taxes.

What does the tax ID indicate?