This sounds awful, sorry you have to go through this.
You mentioned that when you arrived on Aug 2 all bags but yours had arrived.
Two sentences later you say that you guys had filed paperwork, were promised the bags within 24h, and 24 hours later all bags but your arrived.
Were the other bags lost and delivered after 24 hours, or did they arrive with you on your flight?
When you filed the paperwork, did they take a report for your bag that they now claim was never checked? In my experience, you need a bag check record to file paperwork?
this wont help after the fact, but it's never a good idea to check 5k worth of stuff with any airline...!