At this point we are regarding the money they spent for the addition as a "gift" and we will not receive any inheritance. That is agreeable to everyone but who pays for maintenance on the addition? If it is technically our house, and we want to maintain the property value, I'm thinking we pay for regular maintenance? They moved in last December.
If the addition isn't on separate meters for gas, water, electric? Their share is the percentage they represent (as the two of them) compared to the number of people in YOUR household. You have three people, they have two? They pay 40%.
Straighten it all out know. Easier to do earlier on. Good luck! Nice arrangement.
Additions can become tricky. Parents paid for the addition, thus improved the value of your home [unless your home was already the highest price home in the neighborhood]. But it will also make an increase in real estate taxes. I would think you would want full rein of the maintenance so it can be done your way, thus you pay for all the maintenance.
Now if cleaning was part of the maintenance, then the parents might decide to pay for a cleaning service on their part of the home.
Utilities is another story. Do you bite the bullet and pay for the extra water, electricity, heat, air conditioning, or will you figure it out as per square feet who pays what.
Good luck, hope you all can come up with a win-win agreement.