Legal analysis: the purchase contract can be signed by family members, but there must be a power of attorney from the parties, preferably a notarized power of attorney. If it is signed on behalf of the principal without a power of attorney, the contract is of undetermined validity and needs to be ratified by the parties afterwards. If the parties fail to ratify it within 1 month, the contract is invalid for the client. At this point, if the contract has caused damage to the other party, the family who signed the contract should compensate.

Legal basis: Civil Code of People's Republic of China (PRC).

Article 165 If the power of attorney is in written form, it shall specify the name of the agent, the matters to be represented, the authority and the time limit, and shall be signed or sealed by the principal.

Article 171 Where an actor has no agency, exceeds the agency or remains an agent after the agency is terminated, it shall not be effective to the principal without ratification by the principal.

The counterpart may urge the principal to ratify it within 30 days from the date of receiving the notice. If the trustor fails to declare it, it shall be deemed as refusal to ratify it. Before the act committed by the actor is ratified, the bona fide counterpart has the right to revoke it. Revocation shall be made by notice.

If the act committed by the actor is not ratified, the bona fide counterpart has the right to demand the actor to perform the debt or demand the actor to compensate for the damage he has suffered. However, the scope of compensation shall not exceed the benefits that the counterpart can obtain when the principal ratifies.

If the counterpart knows or should know that the actor has no right to act as an agent, the counterpart and the actor shall bear the responsibility according to their respective faults.