Legal rights and best course of action?

Here's the situation: Simon and Suzanne are shown a home by a real estate agent, Warren, selling the house on behalf of the owner, Leslie. Leslie has instructed Warren to sell quickly but for not less than $425, 000. Simon asked Warren whether there was any plan to redevelop the area and declare it “non-residential”. Warren answered: “Not to my knowledge, but I’ve lived in this area all my life and you could not find a better place. Why would they want to destroy it to build a road?”
Suzanne and Simon bought the house for $425, 000 jointly liable on a mortgage of $375, 000. Written contracts were prepared with Warren signing on Leslie’s behalf.
Months later the Queensland Department of Transport informed the owners that their properties would be compulsorily acquired for the construction of a freeway. It then lawfully purchased the land for $80, 000. This is all the compensation that Suzanne and Simon received.
Their bank then pressed for payment of the outstanding mortgage with interest. They were unable to make repayments.

Here's the questions: Is there an enforceable agreement? Is there any common law or statutory protection available for the individuals? Are there any relevant terms of the contract (if one exists)? Has there been any misrepresentation of terms of the contract? Are there any legal grounds to set the contract aside? Has the contract been discharged, if so how? Are there any damages suffered by any of the stakeholders? Are there any relevant remedies?

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