Heat issues at new 4-plex

[Ben S.]

I have a tenant that is going to fill an emergency tenant remedies action on me which means I have 24 hours to fix the issue otherwise they are able to force me to pay for a hotel for them or something like that.  This is all for the heat but I keep the heat in there unit at 71 degrees but they are complaining that one of the bedroom is at 65.  But they also told me that the bedroom that is cold has to always have the door closed because the cat goes in there and pees and poops because it's a mess. 

If anyone lives in MN they know that if you keep a bedroom door shut it will always be cooler than the rest of the house.  So I seriously don't know how to fix this issue.  Does anyone have suggestions on what to do?  I personally keep our house at 69 and our bedroom with the door always open that is upstairs is almost always at 65 and we are more than okay with that.  

I've had multiple professional people look at it and they say it's working but if possible I can install a separate thermostat in each unit to help regulate the heat per unit.  Because I have one of the 4 units that has to open a window to cool it down.  The unit that is filling this claim is the unit with the thermostat in it and it is set at 71.