IntroductionIn order to determine whether John and Sylvia have any legal claim against Peter, we have to determine whether there was a valid contract between the parties and whether Peter was in breach of the contract. To constitute an effective contract, there must be an agreement with consideration and legal intention.
Was there an offer made & who was the offeree?Yes, indeed, Peter had made an offer to John by writing to him(1). As in the case Carlill v Carbolic Smoke Ball Company (The classic authority for unilateral contract)(2), where Mrs Carlill bought and used the smoke ball as specified in the advertisement, the company made a promise in the advertisement to pay and it had deposited some money at the Alliance bank to show its seriousness- unlikely to be a puff.(2) In this case we can establish that Peter had made a promise. To show that he is serious about the offer, (not just a pitiful father trying to gain attention) he sent to John and Sylvia a copy of his will showing that his entire estate will go to John and Sylvia after his death.
Since the offer "to give John and Sylvia a home in Melbourne and his entire estate when he died" was made by Peter (promisor/ offeror) to reward John (the offeree) for his performance of the requirement to help Peter run the house and the estate agency, this is a unilateral contract.
"A unilateral (one-sided) contract occurs when one party makes a promise of "reward" on performance of some action. The offer is accepted by the performance of the requested action. The contract is one-sided because the offeror is required to pay the reward if the act is performed but no one is legally obliged to perform, or even attempt, the act."-a text book...