What strategies should I employ in these negotiations to ensure the partnership is equitable and beneficial for both parties?

My attorney told me because we are a third party there is nothing we can do and that I am at the mercy of seller’s attorney and TC/land surveyors.

So, this is mostly about the motivations of the parties involved IMO. 

See Richards link on BP.Texas Tuesday Mastermind and Party. 1st Tuesday of the month in Fort Worth and Dallas.

Happy to share all information with any interested party even if they are kicking the tires.

Here's how to navigate the information sharing with different parties involved:- The seller: generally, you do not need to disclose your house hacking plans to the seller.

Furthermore, delaying decisions may prevent both parties from pursuing new opportunities aligned with their respective goals.Evaluate your long-term financial objectives and personal aspirations for the portfolio.

DON'T trust a 3rd party on the price unless they have a scope of work from someone qualified to do the job to ensure the quote. 

Also, is there a clause or addendum you use addressing the possibility of the property not appraising for enough when your buyer goes to refi to pay off a balloon and how the parties will continue?

We also own some multifamily ourselves, so we're both owners/operators and 3rd party property management for other owners