Is there a funky property tax issue that arises with the collateral that is a local municipality error and can lender quickly analyze the situation, assess and articulate the risk and allow draws to carry on or will they make the life of the borrower miserable?

On the other hand, you might find a common reason that a few of your potential investors are not investing that might change your own thoughts on the deal.

Is it common to purchase a home with other debt?

If you and another person own a piece of real estate as tenants in common then you both own real estate. 

They didn't know each other before moving in but they all have something in common and they are all grown adults.

There's a specific forum for House Hacking.You'll want to spend some time reading through there as it's a common topic.

If they are on the deed, the property is owned as 'tenants in common'.Is there a tenants in common agreement?

Have I made a terrible mathematical error?

It’s a common practice and I’ve never had any opposition to this provision.If you don’t have an operating company, you could get into contract in your own name and then assign it.  

You could read 100 books and still need to learn more because certain things must be learned through trial and error.