Also last November I bought a single family house that is an airbnb and it has a 1/1 apartment in the back that is a long term rental. 

It's been steadily growing in terms of population, rent rate and appreciation. 

I’m fine with this, for now, as a long-term investor.I don’t believe our current situation would enable us to qualify as Real Estate Professionals, which would result in massive deductions.

Personally, we're okay with properties that cashflow decently, but have long term appreciation upside too.

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.

I.e. is granite acceptable, or does it need to be quartz?  

@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.