I think the title of your thread is interesting. You have titled it 'I keep changing my mind' rather than something like Fear of flying or something along those lines. You say you have thought about moving since you have had children, I wonder if deep down you are still undecided and are using your fear of flying as a reason to not come. Or do you mean you think you can fly to Australia, but then change your mind?
We had similar issues with the in laws. When we discussing emigrating (which wasn't often because they are the kind of people that think if we don't talk about it, it won't happen!) they stated that they wouldn't be able to fly to come and see us because of my FIL's back issues and sitting down for long periods. My dad suffers with back problems and has had an operation and various injections into his nerves to help ease the pain, but he has been out to see us several times, because his motivator is he loves his daughter and wants to see me. When I suggested to the in laws they could come by ship and it didn't matter how long it took because they are retired and they didn't need to rush the journey, this suggestion was met with absolute silence! The reality was they were scared about leaving their comfort zone, had absolutely no interest in going on holiday/visiting Australia and were looking for excuses to not come.
I hope you are able to find a solution whether that means coming to Australia or staying in the UK and being happy with that decision.