The chance that this was an "accident", someone taking the wrong bag went away in the first hour.

The person would have realized their error when they got to Security and found that they did not have THEIR passport and other documents but the OP's daughters and at that point, if innocent mistake would have initiated steps to return that bag and get their own.

No, you can bet that this was deliberate by the time that has passed and thus a less than zero likelihood of recovery.

In addition to filing claims with BA, would their be any recourse via travel insurance or the credit card you booked the trip with to recover the value to lost items?