I think everybody in this situation needs to stop and think "what am I trying to accomplish?":
This whole situation has clearly gone beyond solutions and has become antagonistic and the best course of action is for everybody to just work towards a sort of compromise. However, parents have the final word because their name is on the deed to the house.
Conclusion: I think you're in asshole territory but I think everyone in this situation just needs to do some introspection and think about what's going on here and just work towards something amicable as a group of organized people. I understand why that's frustrating to hear as parents aren't always amicable but that's my assessment.