Can the Aqiqah that the mother vowed for her daughter upon her birth, and then vowed it again for her son upon his recovery, be for both of them?

A vow contingent on a disliked condition is considered reprehensible by most scholars, yet it is obligatory to fulfill it once the condition is met, based on Allah's saying: "And let them fulfill their vows," and the Prophet's (peace be upon him) saying: "Whoever vows to obey Allah, let him obey Him."

Therefore, the woman must fulfill her two separate vows, and a single sacrifice is not sufficient for both. If she is unable to fulfill the vow, she must offer expiation for an oath.