Part of the arrangement was that I could attend the events as well, which was great.

If she was primary, then you would be getting child support or just paying to raise a kid.It is possible with her being married now, that you could go to court and push for a 50/50 co-parenting arrangement, where she no longer pays money. 

For any asset purchase you have to find a deal, due diligence it, negotiate the sale, arrange financing etc.

They told me that people who are staying in a co-living arrangement often are lower income earners, so they struggle to budget monthly.

I have a family member who owns property in a north jersey location,  the property currently has a 99 year NNN lease arrangement to be restructured every 5 years. 

Could a partnership or LLC provide a vehicle for this type of arrangement?

I can ask the sellers if they are willing to extend but from a prior conversation they have arrangements they need to keep.

If you have end buyers and know their criteria, perhaps it can be arranged that they can put up the EMD.

If I want additional marketing for specific vacant units, how would we arrange that?

You can collect bids there from cleaners and arrange meetings with them.