Question about Capital Gain Tax (CGT) moving from old to new to old property....

I would like to ask a question about CGT on behalf and hope you can help me and my family out in regards to accounting issues.

Here's the story. I am living with my dad and brother in Manly house for 15 years+. We were thinking to downsize so last year my dad bought offplan apartment in Dee Why and can move in end of 2015

Originally, they were thinking to sell the house in Manly around completion of the new apartment and then move into the new apartment. However, plans have changed recently as we want to live for 1-2 years and then move back to the current house property.

We heard that if you live a new apartment for 1 or 2 years, then when it is sold, the the capital gain tax will be exempt?

Here's the plan now

When the new Dee Why apartment is finished & ready to move in end of 2015, we intend to move in for (1, 2 years for whatever the capital gain tax will be exempt as main residence) while the house we live in Manly, we will rent it out.

After 1, 2 years, will sell the new Dee Why apartment (without paying capital gain tax?) and then move back to Manly house and I heard if you live for another 1 or 2 years in Manly, then it will become as main residence again and later when sold, then capital gain will not be applied?

Correct me if I am wrong

Your answer will be appreciated!!

Not quite right, you will pay cgt on one or the other. Lots of people who have never owned 2 houses at the same time will tell you otherwise but dont listen to them, speak to an accountant
You are wrong! Only one house can count at the main residence for any one period of time.

One exception. The 6 month overlap/sale rule.

If former home is being sold and you move to new home and former house is sold within 6 months you can treat BOTH as a main residence.