For example incase iIf you identify an asset in the market that already has a realtor representation on both the buyer and seller side, do you reserve the right to proceed with the deal independently, or do you have to bring in your realtor? 

While you can file a partition suit independently, some may strongly recommend working with an attorney for a faster/more efficient process.

We’ve all agreed that living together would be a win-win: they get to gain independence, and I get to start my real estate investment journey.

This is bogus if buyer and seller are independent parties (if the parties are associated then I understand setting true value) as there is usually a reason for the discount purchase (risk items like unpermitted work, crazy low rents in rent controlled area, hoarder, heavy need of rehab, etc).  

A lot to unpack but my overriding 'advice' for what it is worth is to make sure you seperate the values of the park and the tri plex and analyze independantly. 

I would approach a couple of Independent Agents (represent multiple companies) that write both Personal and Business Insurance.  

Always verify and seek independent confirmation of anything you're being sold or told.

I don’t see how he could simply independently come up with such a high price without discussing it with me first. 

Renting for all my independent life now, I've noticed rentals I've found were on certain platforms being advertised, like craigslist, apartments.com, Facebook marketplace, and landlords posting to their personal social media accounts.However, I can't imagine these avenues being the only advertising methods, when you have something like vacancy to fill.

Find a commercial independent broker, they’ll get you on the right track.