Tenant Rant

I think you should talk to BOTH of them together in a nice way, concede a little of the responsibility for the fact that you were not very clear with your expectations...let them know you want a good relationship with them...and say, here's the deal, no lower than 72 while you're at home, and put it up to 78 while you're not at home. If you put a lock box on it without first trying to reason with them, they are going to be disgruntled.