Is it permissible for someone on whose behalf an Aqiqah was not performed to participate with two shares in a cow for Udhiyah: one for the Aqiqah and the other for the Udhiyah? And is an Aqiqah obligatory for the deceased if it was not performed for them during their lifetime? And is it obligatory to repeat the fasts of the days on which a fasting person swallowed stomach acids that reached their mouth during prayer?

It is not permissible to combine the Aqiqah (definition) and the Udhiyah (definition) due to the difference in the purpose of each. Therefore, a sheep should be slaughtered for the Aqiqah for the female child, as this is the Sunnah (definition). The Aqiqah is a non-obligatory Sunnah, and it is good for the family to perform Aqiqah for the deceased if he had not performed it for himself. As for swallowing phlegm intentionally, there is a difference of opinion regarding it, but the relied-upon view is that the fast remains valid. Swallowing it unintentionally or due to an overwhelming urge does not invalidate the fast, by consensus.