Sounds like the pax already confirmed the new flight, extended their holidays and booked Airbnb, i,e. rebooking now to an earlier flight is no longer feasible. Better enjoy the 2 add. days in the US on the account of BA. Most likely reasonable expenses will be reimbursed by BA without fuss afterwards.

No comp. for cancellation is due as pax were notified at least 14 days out.