The only options that I see are rent by the room, mid term, short term, or just putting more money down.

Trying to figure out what their pain point is to see if terms might help. 

My goal in the long term is build up enough equity/extra income to retire at 50.

FYI we've changed our approach entirely and have lower fee initial entry points to avoid the challenges of long term project based arrangements so we can catch issues much sooner.

@Nick Pamintuan I would start with understanding what each of the six partners (including yourself) bring in terms of value to the partnership.

My goal is to at least match my current monthly expense of $3k (After all units are rented) while aiming for long-term appreciation.

Though it is a negative cashflow move in the short term, I fully anticipate rental rates to catch up to the expenses in about 3-4 years and break even monthly.

Now, that might be moot as they can always dissolve the entity and distribute the property in the year they inherit this, but it will be imperative for the beneficiaries to understand THEY NEED TO DO SOMETHING, or else you’re simply giving them the same problem if they do nothing.To reinforce @Jason Watson’s comment: corporations are downright unpleasant for appreciating long-term assets.  

Lightstream is the most famous, but the longest term they lend is 7 years.

My investor friend has a lease option on my property to assume my mortgage and property so she can get the terms, while giving me $30,000 over two years for the option to assume my mortgage and property.