Very unfortunate chain of evens for the OP's parents - and a good lesson (although we probably al do already
) to check flights and tmings directly via the airline(s).
As for the actions of the travel agency - this could potentially be a case of negligence.
Did the travel agent owe a duty of care (yes, probably), did they breach that duty (MAYBE - we dont' know exactly what happened for sure), was there a loss? (yes the cost of the new tickets).
I say the agency MAY have breached their duty because we just don't know what actions they took to get in contact with the passenger, or to advise the passenger of their recommendation to cofirm all flights with the airline prior to departure. Did the agent try and email? Did they phone (but the call was missed)? Did they have the wrong phone number or conact details? Lots of factors.
As for the terms and conditions - they would seem to be fairly clear. But again, as we have discussed before, not all terms and conditions will be binding. Certain vitally important clauses may need to be brought to the attention of the consumer in order fo thm to have effect. OR, possibly not... for example if the consumer is a frequent flyer then they should be deemed to know about certain clauses without having to have them pointed out each time.
A simple way for any agency to do this is to sit with a pen (if you are face to face like at Flight Centre) and they circle the key terms for you (I have had this happen once or twice). This covers them.
On line, it might be that best practice would be that an agency has separate check boxes for the more important terms (instead of just the single 'I/we have read and agree [to the 20 pages of fine print following]')
Then of course the actions of the consumers in this case need to be considered. Were they aware (or should have been aware) that they reasonnably ought to have called each airline to ensure flight times? (and therefore should shoulder some blame?)
however in this case, and especially in the day of the internet, if the OPs parents had checked their first flight via the CX website, or Melbounre Airport site it would have shown as 'on time'. Mere departure information does not show that you have actually been moved to a different flight.
And arlines these days tell you that you don't need to reconfirm.
So lots of issues and will be interesting to see how it pans out.