Testamentary succession If the brother and sister are testamentary heirs, they need to sign; If not, they don't need it. After the beginning of inheritance, the heir who knows the death of the decedent shall promptly notify other heirs and executors of the will, and the administrator of the estate may receive remuneration in accordance with the law or the agreement.

Legal objectivity:

Article 135 of the Civil Code: A will written on behalf of others shall be witnessed by more than two witnesses, one of whom entrusts others to write on behalf of others, and shall be signed by the testator, agent and other witnesses, and marked with the year, month and day.