Parents are draining us! Help! Advice!

My SO’s mom and dad recently moved into our house back home as we moved two hours away a little over 1 year ago. Their house was somewhat hit by a tornado and messed some things up. So while renovations are being done they stay at our house. All of the bills are still in our name and my husband pays them. Due to the fact they run the air conditioner all day with doors open the electricity bill is 200-300 dollars every month. We had a smart thermostat therefore my husband could somewhat intervene but his dad changed the thermostat yesterday. We can’t afford to pay these outrageous bills but he still put us in that bind because he’s scared to tell his parents to switch the bills and pay them on their own. How do I kindly advise him to do so? I know they can more than afford it so there isn’t any problem there. I just can’t keep seeing him stressed to the max over these crazy ass bills!! HELPPPPP!