Who is the one required to slaughter the 'aqīqah?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
It is Sunnah for the 'aqīqah to be slaughtered by the guardian of the newborn — the one upon whom the child's financial maintenance is obligatory — provided he is financially capable of doing so. 'Alī ibn Abī Ṭālib, may Allah be pleased with him, reported: "The Messenger of Allah ﷺ performed the 'aqīqah for al-Ḥasan with one sheep." — Narrated by al-Tirmidhī. And Allah Almighty knows best.
What is the ruling on one who slept while firmly seated on the ground, regarding nullification of ablution?
The default ruling regarding sleep is that it nullifies ablution. An exception to this is one who slept while firmly seated on the ground; his ablution is not nullified by sleep if he wakes up while still firmly seated on the ground. And Allah the Almighty knows best.
Is it permissible to fast the six days of Shawwal before making up for the missed fasts of Ramadan?
● If a person missed fasts due to a valid excuse, they may fast the six days of Shawwal before making up for Ramadan fasts, because qada (makeup fasts) in this case can be delayed, while the six days of Shawwal must be observed within Shawwal.
● However, if a person missed fasts without a valid excuse, they must make up for the missed fasts immediately after Eid, before fasting the six days of Shawwal. If they fast the six days first, it is valid, but they must still make up for the missed Ramadan fasts afterward.
It is also permissible to combine the intention of qada (makeup fasts) and the six days of Shawwal in one fast. However, it is better to fast them separately, as this increases the reward and avoids scholarly disagreement regarding combining intentions.
Is it permissible to trim the eyebrows if they become excessively long?
Trimming eyebrows is permissible if they become excessively long, yet; it is reprehensible. And Allah Knows Best.