Hi
If you go on their website, click on itineraries & check in, then go to my itineraries, you can log on as a guest with your e-ticket number (from your flight details) & surname. Once it comes up with your booking you can select seats etc.
I know JY have seats allocated to them which probably don't show up as being available so you could wait until check in.
Do the travel money cards work like debit cards?
Caroline