Answer:
In these circumstances, it is unlikely that legally enforceable contracts have been concluded with everyone who has complied with John's offer.
(a) John's wife Gen is considered a household member, and thus cannot enter into a contract with her husband.
(b) John's ex-wife Flora, however, can enter into a contract with John.
(c) John's colleague Sam can also enter into a contract with John as they have a professional relationship.
(d) John's son William is a minor, and as per the contract law, a minor cannot enter into a legally binding contract.
(e) John's next-door neighbor Billy is a lunatic, and as per the contract law, a person of unsound mind cannot enter into a legally binding contract.
In conclusion, only John's ex-wife Flora and his colleague Sam have entered into legally enforceable contracts with John for the removal of rubbish and cleaning of his garden.