Subject to the provisions hereinbefore contained, the aid annuities hall continue,
    (a) in the case of a minor son or a minor nephew, till he ceases to be a minor;
    (b) in the case of a daughter or widow, till she voluntarily leaves the household of the heir or legatee of the deceased, or would, according to the custom of the country, cease to be entitled to maintenance, and
    (c) in all other cases, till the annuitant dies.