Does capital gains tax apply?

Q.

My sister and her husband have recently moved interstate for two to three years. Whilst there, they are renting out their home. Will they have to pay capital gains tax on their property if they sell it within the next two or three years, or when they return from interstate?

Provided you do not claim any other property as your residence you can be absent from your home for up to six years without losing its CGT exempt status.