SYDMUM - not to be mean but whatever you do dont get your hopes up - i think it would be a 99.9% chance they will let you keep your holidays - and if they did its unfair to current crew who miss out on slots.
Bid slots have already closed for april and the only way you will get some is if you can bid for another slot for the bid period (if there is a slot left) and find someone to swap 2 weeks with you (highly unlikely as its hard enough to get a slot let alone one you really need)
Sorry - but more likely they will say that they may let you defer to a later ground school if you really cant not postpone your hols.. but they are not that forgiving.. in the past people have had to reschedule weddings and funerals to fit in with their annual leave (or lack of) and they def dont do leave without pay for any reason - at all.
Just giving you a heads up so you can start thinking about what you want to do.