Is the son of the sister by breastfeeding considered a mahram in Islam, and is it permissible for a woman to go for Hajj with him?
Everything that is prohibited by lineage is also prohibited by breastfeeding. The son of the sister by breastfeeding is considered a mahram, just like the son of the sister by blood, and it is permissible for him to be her mahram for Hajj and Umrah. And Allah Knows Best.
How is the meat of the 'aqīqah to be distributed?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
If the 'aqīqah is a recommended one (mandūbah), it is obligatory to give some portion of it in charity to the poor — even if the amount is small — with the minimum being approximately half a kilogram of meat.
The most preferable manner of distribution is to divide it into three equal portions, as with the uḍḥiyyah:
One third for the guardian and his household to eat from
One third to be given in charity to the poor
One third to be gifted to friends and neighbours, even if they are wealthy
It is furthermore more preferable to send the food to the poor already cooked, rather than inviting them to come and eat. And Allah Almighty knows best.
What is the ruling on sacrificing a castrated animal or one with a missing tail?
Praise be to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is permissible to sacrifice a castrated sheep; as it has been established that the Prophet (peace be upon him) sacrificed:
"...two large, fat, horned, white-and-black, castrated rams (Mawju'ayn—meaning having crushed testicles)." [Narrated by Ibn Majah in his Sunan].
It is not permissible to sacrifice an animal that is missing its tail, rump, or udder due to being cut off. This is in contrast to an animal that was naturally born without a tail, rump, or udder; such an animal is valid for sacrifice. And Allah the Almighty knows best.
What is required of a traveler or a sick person if they broke their fast and then their excuse ceased?
If a traveler settles or a sick person recovers after having broken their fast, it is recommended for them to refrain from eating and drinking for the rest of the day, but it is not obligatory.