What a lovely son you are...your parents have done a great job in raising you.
Which is why I'm sure they wouldn't want you to forego such a great opportunity.
Sadly, it's a fact of life that our parents will age and pass away some day. But we can't sit around waiting for it to happen. You have to live your life and take the opportunities that come your way.
I also moved to Australia shortly after getting married. At the time, my parents were in good health and able to visit. We spent a lot of time together when they came out to visit (more in one go then than back in the UK). I have great memories of those visits and often our time together was quality rather than quantity.
Now sadly, my Mum is gone but I look to my own children. They're still little now but I know I'd hate them to turn down any future opportunities because they were worried about leaving me.
Talk to your parents about how you feel. Show them this post. See what they have to say about it.
And as others have mentioned, it's a temporary visa at this stage. Nothing is set in stone. Take it one step at a time and see how it goes.
Good luck...it sounds like a fantastic opportunity.