Is it permissible to give multiple mudds (portions) of fidyah to a single person?
Yes, it is permissible to give multiple mudd of fidyah to a single person, because each day of fasting is considered an independent act of worship.
Is it recommended (mustaḥabb) for the one offering a voluntary sacrifice (uḍḥiyyat taṭawwuʿ) to eat from its meat?
Praise be to Allah, and prayers and peace be upon our Master the Messenger of Allah.
It is recommended (mustaḥabb) — not obligatory — for the one offering a voluntary sacrifice (uḍḥiyyat taṭawwuʿ) to eat from it. Allah Almighty says {what means}: "So eat from them and feed the desperate (qāniʿ) and the beggar (muʿtarr). Thus We have subjected them to you that you may be grateful."— [Sūrat al-Ḥajj (22): 36]
Explanation of terms:
Al-Qāniʿ — the poor person who does not ask people for money, food..eccetera.(beg)
Al-Muʿtarr — the poor person who does ask people for money, food..eccetera (begs)
And Allah Almighty knows best.
What is the ruling on wiping the white area behind the ears instead of wiping the head?
The obligation in ablution is to wipe some of the head; it is not a condition to wipe all of it. Wiping the white area behind the ears suffices for that. And Allah the almighty knows best.
What is the ruling on eating or drinking forgetfully during the day in Ramadan or during voluntary fasting?
Whoever eats or drinks forgetfully while fasting, whether in an obligatory or voluntary fast, should continue their fast, for it is Allah who has provided them with food and drink. There is no difference between obligatory and voluntary fasting in this ruling.