Generally better not to post personal information to a public forum.
If you want to get more Fetch boxes then just contact Optus directly (LIVE CHAT online 24/7) and request them.
Please visit this page for Fetch Multiroom
as per @Ray_YC annd @petergdownload contact optus to have the fetch box (usually the mini) link to your account and send out a new box. Once that is done, connect your new fetch box to the same network as your fetch mighty. The system then discovers itself and you can have the same access as the Mighty for the minis, can even watch the recordings from the mighty. Saying that some records only works on the mighty.
I am not sure how many box you want to have on the same connection, I've tried 1 mighty and 2 minis and that is about the max I would go or fetch allows. Any more will slow your connection right down especially if you are watching 1, recording 2 and have 2 minis in the other room. I found having 3 going at the same time, makes other use's connections much slower even speedtest shows I am getting over 60Mbps with 3 fetch boxes running.