So long story short, years ago me and my middle school "best friend" decided to get out parents together as a joke and now they're married and live at my dads house. I have my own place. So anyways, my dad has been through hell w my two step sisters - he even took parental rights when my older step sister got her taken away and watches her when she goes on her week- month long binges where nobody knows where she is. The sister that is my age stayed home while the rest of the family went up north for vacation for 4 days & I took the dog back to my apartment to watch him. Well, my fiancé just went to drop the dog back off because we can't have him in our apartment & they come home today & my dads house is destroyed. Cigarette butts all over the lawn (it's a condo so that's not even our property) and all over the front porch, cans & boxes everywhere, 4 cars parked there but my sister was just passed out on the couch. I just find it so disrespectful because she's always talking about how much she hates it there & yelling and screaming at my dad and her mom (she's 22) and then pulling shit like this. They feed her, they pay her bills, they help her with her car. None of which I get anymore lmao and she's a year older than me. So now I'm stuck at a cross roads of whether I should warn my dad or just let it play out and give her the chance to clean it up and hope that nothing was stolen. My dads the kindest person ever and I feel horrible that he has to put up with this kind of shit. (Most of its already been pawned by my other sister anyways, including my deceased mothers wedding ring) Any thoughts on what I should do? Leave it or warn my dad what he's walking into after vacation?

Update - my fiancé went over there after work to clean and asked her to help and she pretty much told him to fuck off so I told my dad.