Who is obligated to fast?
The one obligated to fast is the Muslim who is of sound mind, mature, capable of fasting, and free from obstacles such as menstruation or postpartum bleeding. And Allah Knows Best.
Does offering Udhiyah (Offering a Sacrificial animal at Aid Al-Adha) avails from offering Aqiqa?
Offering an Udhiyah doesn't avail a person from offering Aqiqa because each of which is a different act of worship. And Allah Knows Best.
Are all the children of a suckling woman considered brothers to the strange child whom their mother had breastfed, or just to the one who had suckled with him?
All the children of the woman who had suckled a strange child are considered his/her brothers and sisters.
I became ill while fasting and had to take an intramuscular injection twice on two consecutive days during Ramadan. I continued my fast as usual, as I was told that intramuscular injections do not break the fast. Please advise me so that I can know the correct ruling.
Subcutaneous and intramuscular therapeutic injections are not considered as invalidators of fasting because they do not enter the stomach through an open passage. However, intravenous injections containing nutritional fluids do invalidate the fast, as they are akin to food and drink in purpose. Therefore, your fast is valid. And Allah Knows Best.