Are minors obliged to fast?
A male under the age of puberty isn`t required to fast, but his guardian should order him to fast if he was able to endure the hardship until being used for fasting in general. And Allah Knows Best.
What is the ruling on the unification of Adhan?
All perfect praise be to AllahThe Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions. The unified Adhan is an act of Sunnah performed on behalf of a city's population. In addition, any Masjid that doesn’t have a Mua'than (The person who calls for prayers) and doesn`t raise the Adhan misses the reward of this great act. This is because Adhan should be raised for every group of people. However, the unified Adhan should be called in one Masjid and heard through all other Masjids. And Allah Knows Best.
Is it permissible for the big brother to force his sisters to wear Hijjab (Islamic wear) if their father didn`t do his part in this regard ?
All Perfect Praise is due to Allah, The Lord of The Worlds
The father`s attention should be drawn gently and politely, and the sisters should also be reminded with good words since Allah, The Almighty, Says (What means): "O ye who believe! Save yourselves and your families from a Fire whose fuel is Men and Stones." [Al-Tahreem/6]. And Allah Knows Best.
What is the Time for Making up Fajr Prayer and Other Missed Ones?
All perfect praise be to Allah The Lord of The Worlds and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his familty and companion.
The Messenger of Allah (PBUH) said: "Whoever forgets a prayer, let him perform it when he remembers it." [Muslim]. As soon as you (Questioner) wake up, you are obliged to make up the missed Fajr prayer. And Allah Knows Best.