Is it permissible for a woman to observe voluntary fast without her husband's permission?
A woman is not permitted to observe a voluntary fast (nafl) while her husband is present without his permission.
Is it permissible to offer mandatory prayer while sitting?
All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his family and companions. Standing up is a pillar in the mandatory prayer and the prayer is not valid without it unless one cannot do it. As for Nafila (supererogatory prayer), one can perform it in the state of sitting even if he/she can stand, but his/her reward is half the reward of the person who prays while standing if he/sh has no legal excuse for such an act. And Allah Knows Best.
Which is better during the day in Ramadan: reciting the Quran or performing voluntary prayers?
A Muslim should establish a daily schedule for reciting the Quran in Ramadan.
Once they have completed their daily portion (known as a wird or hizb), they can engage in other acts of worship, including voluntary prayers (nawafil). Prayer itself is called "Quran", because a significant part of it involves reciting the Quran.
Allah says: "BE CONSTANT in [thy] prayer from the time when the sun has passed its zenith till the darkness of night, and [be ever mindful of its] recitation at dawn: for, behold, the recitation [of prayer] at dawn is indeed witnessed [by all that is holy]." [Al-Isra`/78]
What is the ruling on eating from one`s Udhiyah?
In the Name of Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
The Udhiyah (sacrificial offering) is divided into two categories: the vowed sacrifice (Al-Mandhurah) and the voluntary sacrifice (Al-Tatawwu').
First: The Vowed Sacrifice (Al-Mandhurah)
This refers to a sacrifice that has become strictly obligatory due to a formal vow (Nadr). It is completely impermissible for the person offering it, or any members of their family whom they are financially obligated to maintain, to eat any of its meat or fat. Furthermore, it is unlawful for them to personally benefit from its hide, wool, or any other part of it. If they happen to eat any portion of it, the offerer is legally obligated to give an equivalent amount of meat or its monetary value to charity. (As noted in Tuhfat al-Muhtaj by Imam Ibn Hajar al-Haytami,Vol. 9/P.364).
Second: The Voluntary Sacrifice (Al-Tatawwu’)
This is a recommended, non-obligatory sacrifice. The person offering it is fully permitted to eat from its meat, distribute portions as charity to the poor, and give pieces as gifts to those who are well-off. However, it remains a mandatory requirement to donate at least a minor portion of it to charity; this should not be less than approximately half a kilogram of raw, uncooked meat. And Allah the Almighty Knows Best.