B) there is a court case that says permitting subtenants shall not be unreasonably withheld.

From what I see here, they are not being unreasonable in their requests.The late rent situation is an entirely a separate issue.

I had a tenant like that once it is better to offer them there deposit back and move on to the next tenant.It will not end for them to request unreasonable repairs.  

As for the heat, as mentioned above you should have addressed the heating situation on the front end; it's unreasonable to expect one tenant to control the heating/cooling for 3 other tenants in separate units. 

& repairs is unreasonable, toss taxes, trash and whatnot into the pile and the expense are easily beyond 50% of the income.I'm just guessing the 50% rule just doesn't work as well for lower income numbers in calculating profitability.

It would be unreasonable to believe you're going to quit your job off of 15 properties leveraged @80% bringing in $200/door.

There is no sense working with someone who's making unreasonable offers, and hasn't had one accepted in 6 mo.s.

Looking at it from the Vendor's perspective, if I am looking for a cash buyer, a 10% EMD is not unreasonable.  

I don't think I would want to partner for less than 50% but I wanted to make sure that I wouldnt be making an unreasonable offer.

Is it unreasonable to ask if they would be interested in financing it to me?