Visiting or staying parents

I would prefer for my parents-in-law or even my parents to stay wtih us once we're there. But how?

If they apply to visit us, how many months will they be given for their visa? If it is only 3 months and I make an assumption that they would be visiting us 3x a year (3mths each), that would cost us $6K on airfares (1K x 2persons x 3 visits). Is it possble to get 6-months visit pass? Is it possible to extend a visitor's visa when a visitor is in Australia?

I read about Sponsored Family Visitor visa (subclass 679) but it seems to be more unnecessarily complicated if they could only get 3-mths visit terms, similar to visitor's visa. It requires certain security bond ($). But I'm not sure if this visa would help subsequently when we try to apply for residency for our parents.

In the end, we wish to have our parents to stay with us without having to travel in and out of the country. They may get older and travelling would be more and more difficult for them. But I think it would be a long journey to reach there and there's a possibility that they won't even get the residency.

If we decide to leave for Australia sooner, it will be a good idea too so we could satisfy one of the conditions for our parents' residency application, i.e. that we have stayed in Australia for 2 years. I hope my hubby's brother will also go to Australia soon so all my PIL's children are in Australia and their apoplications will stand a better chance.

Until then, our parents will have to travel up and down Singapore-Australia. They would stay with us when in Australia and stay at their other son when in Singapore. Luckily, they are still very active, healthy and strong (they could outrun me and my hubby in any running events), and they love to travel.