Is the father a Mahram (Non-marriageable) to his son`s mother-in-law?
The father is a non-Mahram (Marriageable) to his son`s mother-in-law, so it is impermissible for them to look at each other, or to have a seclusion (Khalwah).
When does the time for the 'aqīqah lapse and pass?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
If the guardian was financially capable (mūsir) during the majority of the postnatal period (nifās) — which is sixty days — then the obligation of the 'aqīqah remains upon him until the child reaches the age of maturity (bulūgh). Once the child reaches maturity, the demand falls away from the father and those like him. At that point, it becomes Sunnah for the child himself to perform the 'aqīqah on his own behalf.
However, if the guardian was financially incapable (mu'sir) during the postnatal period, and then became financially capable after its expiry — that is, after sixty days — the 'aqīqah is no longer required of him. And Allah Almighty knows best.
What is the ruling on eating from one`s Udhiyah?
Praise be to Allah, and peace and blessings be upon our master, the Messenger of Allah.
Sacrifices (Udhiyah) are categorized into two types: the Vowed Sacrifice (Al-Mandhurah) and the Voluntary Sacrifice (Al-Tatawwu').
1. The Vowed Sacrifice (Al-Mandhurah)
The vowed sacrifice is obligatory due to the person’s specific oath. It is not permissible for the person offering the sacrifice, nor for those they are legally responsible for financially supporting (dependents), to consume any part of its meat or fat. Furthermore, it is not permissible to benefit from its hide, hair, or any other part.
If they do consume any part of it, they are required to give in charity an equivalent amount of meat or its market value [Tuhfat al-Muhtaj, by Ibn Hajar al-Haytami (9/364)].
2. The Voluntary Sacrifice (Al-Tatawwu’)
Regarding the voluntary sacrifice, it is permissible for the one offering it to eat from its meat, distribute it as gifts to the wealthy, and give it as charity to the poor.
The Obligatory Portion: It is mandatory to give at least a small portion of it in charity to the poor; this portion should not be less than approximately half a kilogram of raw meat. And Allah the Almighty knows best.
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.