I was watching a video of soldiers being repatriated
and every one seems to salute them - do soldiers
of every rank salute fallen comrades or are there rules ?
The Australian soldier was awarded the Australian VC which is a different award from the British VC. I don't know whether British soldiers would salute this any more than they would salute the US Medal of Honor. Regarding saluting fallen soldiers, in my experience it is a sign of respect that would be accorded to anyone including enemy if they had fought and died honourably.
Strictly on a technicality, no one is "entitled" to salute unless s/he is in military uniform wearing their headgear. The rank is irrelevant because that's not what's being saluted, it's the armed forces of the monarch.
Unofficially, there's nothing/nobody to stop you doing it.