Quote ="Leyther Nutter"are we better buying our train tickets online or just pay on the day (the same for us getting from Toulouse to Carcassonne)'"
Sometimes there are better deals if you buy in the UK for French trains. But these distances are so short it shouldn't make difference. Buying tickets at the station is dead easy.
Some trains though (the TGV for example) are reservation only so depends on which train you want to take.