For two weeks I wouldn't recommend more than Sydney & Melbourne.

My suggestion would be to move your holidays to after the wedding. Things will be much cheaper as this will be outside school holidays.

Maybe spend 5 nights in Melbourne (including a few days trips to the surrounds) - drive yourself to Sydney along the great ocean road (this can be done in a day but recommend two). Then 7 nights in Sydney (including say two in the blue mountains). Don't bother with going too much further north. It will be hot and humid in Queensland and it really is not the best time to visit the reef if that it what you were planning.