Yah...I understand.
My mom does that too. I am only thankful she cannot afford to fly
us anywhere. But everywhere in our lives, you see her making those
sort of decisions for us, then tells us later.
Then when we grumble, she goes all drama, teary and cry heaven cry
earth and we are ungrateful children issues all come out. Hope
yours not as dramatic. 
Try ask for the tour agency, and call them yourself to do a
postphone, so your family can fly to Perth while you are flying
back to Oz ? Maybe re-route your flight to Melbourne into Perth for
them? Bring forward your trip back to a week before you were due
back. So you can bring your family around.
That should hopefully solve your time issues?
