Hi Maria
I had this exact situation a few years ago.
Whilst the pensioners are required to contribute to rates and charges per the contract, they are not the owners of the property. Oak Tree Retirement Village is the owner and under section 560 of the Act they are liable for payment of Council rates.
The question to ask is if the rates were unpaid who would you take legal action against? It would be the owner as per section 560.
The other thing is to is Council is not bound by the contract as they are not a party to it.
Hope this helps
Robert