From what I understand is that the pets will have a lay over some place like Germany because the flight is so long. The best bet is to contact the embassy and airlines for more info on that, I do know for sure though that they will have a stop at some point because it is inhumane to keep them kenneled for so long.
Next because you do have older pets, I HIGHLY suggest NOT giving a sedative. I don't recommend giving them at all even for short flights. There are natural remedies that you can give to help relieve stress, but I would avoid any sedatives or tranquilizers.
Next I'm sure that Tasmania has a quarantine that follows Australia, here's a link to the quarantine laws, and what is posted there
Here's an email for the quarantine that you can contact in regards to your questions also: Quarantine.Enquiries@dpiw.tas.gov.au
Here are also so more links that can help you, the second one should be where you will find the most info