Hi Rob,
The apartment / new build has died a bit of a death at the moment with oversupply, we've just finished 100 nr 2 bed units in south Perth and the client has not sold a single one. Construction work is still happening but work has definitely slowed down. The good news is you have a trade so should be able to pull in some work, however without the correct certificates it may be hard going.
Just a thought but you should come out here for a couple of weeks on your own and walk round some building sites, line up some interviews, start answering some ads (it's a heck of a lot easier getting an interview when you are out here rather than calling from the UK, get a cheap mobile with an aussie number to get you started) All it will cost is the air fare and a few weeks rent. It worked for me.
I've been here 4 years now and do not regret the move one bit. I've four kids 15 to 21 over here so bit older that yours but they absolutely love it. The school the two boys go is private but £5k a year for both of them so miles cheaper than the UK and they actually enjoy going there. There kids at school are all pleasant, polite and whilst the school is very strict, the kids still have a great deal of respect for the teachers which is great to see. In my experience we are so glad we have bought our kids over here, they had a rotten time in the UK with a terrible school and the eldest ones had no chance of finding work. All 4 of the are now working out here ( boys part time in KFC) it's great to see them developing and enjoying going out with some money in their pockets. Yes there are plenty of their mates that stay in on the computers all weekend, my sons included but then that is your job to then pull them away from that and get them involved in other activities. I recently joined the local yacht club ( £250 a year full membership and use of the training dinghy's) and we take the boys sailing every Sunday morning, they are taught by local kids their age who take them out. That would never of happened in uk ever, the opportunity just wasn't there.
It is hard but i walk the dog on the beach with my wife most evenings so there are some consolations.
Hope the above helps
Cheers