Honestly, the biggest lesson here seems to be that cleaning out a family home is rarely just a cleaning job when there is already unresolved family tension involved. Your dad may have genuinely thought he was helping, but moving someone’s belongings without their permission, especially while they still have the right to occupy the room, was almost guaranteed to create another argument.

If everyone had agreed on a simple plan beforehand, your sister decides what stays, what goes, and when she wants to remove it, the whole thing could probably have been handled without nearly as much drama. When a house is being emptied during a separation or move, getting the physical work organized separately from the family disagreements can make a huge difference. A professional move-out cleaning service can even handle the actual cleaning once the belongings are gone; RMS Cleaning, for instance, offers move-in/move-out and deep-cleaning services for situations where you just want the property cleaned without adding another family member to the argument.

As for your position in all this, I actually understand why you don't want to become the referee. You can help your dad, mom, or sister when they ask without taking responsibility for decisions they made themselves. The important part is making it clear that helping move a box doesn't mean you're taking sides. Your family can sort out the emotional and legal issues between themselves while you concentrate on getting your own loft finished and staying out of the crossfire.