This probably wont help but it my opinion those kids need punished for every single little thing that is broken or missing
I have two kids My brother 11 and my sister 17. As you can guess sometimes they think they can fun over me because im not mom but I wont let it slide.
Last week they lost the dustpan (one of them was cleaning and it got shoved under the couch) I made them sweep the kitchen with the mini broom (
Cleaning Products Mini Dust Pan & Brush Set (Pack of 24) Pack of 24 )
And then they found the dustpan I am very strict with my kids If one of them back talks no friends and no tv/computer for a week I even had to take books away from my sister
the only thing to do it lay down the law