It happened to us on the way back from NYC. We were relegated from the upper deck to lower deck seats because one of our seats was faulty. One of us could have stayed upstairs because the other seat wasn't broken. We both moved downstairs and when we got home, we completed the form on the BA website. Within around 14 days both seat reservation fees were returned to our account. We were fortunate to be moved to an aisle and window seat together - it's shame that your parents are being separated but if the seat is possible broken it might be there is no other choice?