Is it permissible for a person to give the Zakah (obligatory charity) to his daughter-in-law?
Yes, it is permissible for a person to give the Zakah to his daughter-in-law if she was poor, and none provided for particularly by whom are obliged to provide for her. And Allah Knows Best.
What is the ruling on making up missed fasts from many years?
A Muslim must make up for any missed fasts, as they are a debt owed to Allah. The Prophet ﷺ said:
"The debt owed to Allah is more deserving of being fulfilled." [Narrated by Muslim]
Whoever has missed fasts must make them up as long as they are alive and capable of fasting.
Is it permissible to purchase the Udhiyah on installments?
It is permissible to purchase the sacrificial animal (uḍḥiyyah) on installments or by borrowing its price. However, it is not recommended for the poor to do so, because they are not required to offer a sacrifice, and Allah does not burden a soul beyond its capacity. If doing so would lead to negligence in providing for one's dependents (nafaqah wājibah), then giving precedence to obligatory maintenance over borrowing to buy the sacrifice is appropriate. This is based on the saying of the Prophet (peace and blessings be upon him): "It is sufficient sin for a person to withhold food from those whom he is responsible to support."
Furthermore, the sacrifice is valid from one who has a debt, but it is preferable (awlā) to repay the debt first, especially if the debt is due immediately (ḥāll). And Allah Almighty knows best.
Is it permissible to appoint a proxy for the sacrificial offering outside Jordan?
In the name of Allah; all praise is due to Allah, and peace and blessings be upon the Messenger of Allah.
It is permissible to appoint a proxy—whether an individual or a charitable organization—to perform the sacrificial slaughter (Udhiyah) on one’s behalf, even if it is carried out in a country other than that of the donor. This is conditional upon the proxy’s adherence to the established requirements of the Udhiyah, including the animal’s age, its freedom from physical defects, the designated timing of the slaughter, and the proper distribution of the meat.
However, it is preferable for the one offering the sacrifice to perform the slaughter personally, in order to attain the full reward and blessings of the act. And Allah (Exalted be He) knows best.