Lynn-ann

Hi, I'm Australian waiting for my husband of 11 years to get his spouse visa. Now my problem is I have three children born in England. Their ages are 23,21 and 18. I found out alittle late that I could get them registered citizins by decent before they reached 18. The only one I managed to do this for was the youngest just before his 18th birthday, so he now has his Australian passport.
Here's where my problem lies my 23 year old want's to come with us. He is going to get a working holiday visa and do some traveling, what then? Does he have to come back to England and apply from there or can he get an extension to the visa and apply in Oz? Any advice. Please.
Thanks