Can I just add... if your parents stick with the fly GLA-MAN option, not only are we £3 cheaper than BA, but we use an Embraer145, BACX (as of this week anyway) are using DHC-8s, so we usually get there about 10-15 minutes quicker! Our gates are a shorter walk too...
A serious suggestion: give them the bmi web address, then have them search for flights themselves... I've noticed with searching from the US that the same tickets sometimes work out cheaper. It is certainly worth a try to see if they are also cheaper when ordered from Canada.