I found the Product Specification yay!

if you are unable to make your repayments, for any reason, the guarantor is required to make repayments on your behalf. If repayments are still not met and the bank has to foreclose on the mortgage and sell your house, the guarantors are responsible for paying the bank any money that the bank has lost on the sale of your house - if that means that the guarantors have to sell their house as they do not have the cash then that is what has to happen.
That would be up to the amount that they specify:

from http://www.partners.stgeorge.com.au/...ion%284%29.pdf
The guarantee is structured so that the guarantor's liability is limited to a specified amount and, at the request of either the borrower or the guarantor at any time during the loan term, they can ask to be released from the guarantee.
...
This structure will provide the guarantor with certainty of the value of their guarantee and allow them to have their property released much earlier than would normally happen.