Thanks for all the useful feedback so far, everyone.

After some initial sniffing, I can see two C-class tickets available around a time we'd like to fly. Is there merit in snapping these tickets up and then praying to the Gods that two more (1st or Business, any combo) will be released in the interim?

It's a game I wouldn't mind playing if if was just me and the missus flying, but I don't want to leave my mum n' dad in the lurch if seats fail to appear!