Is the woman who do breastfeeding permitted to break the fast during Ramadan?
It is permissible for pregnant and breastfeeding women to break their fast during Ramadan if they fear harm to themselves or their child. However, they must make up for the missed fasts. If the fast is broken out of concern for the fetus or the baby, expiation (Fidya) is also required along with making up the missed fasts. The expiation involves feeding one needy person with an amount equivalent to a Mudd of food (approximately 600 grams of wheat or rice) for each day of missed fasts. If the fast is broken out of concern for the woman's own health, only making up missed fasts is obligatory. 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.
Is it permissible for someone to make a supplication to Allah to marry an already married, or an engaged woman?
No, it isn`t, and the person who does so is sinful before Allah, The Almighty.
Is it permissible to combine and shorten prayers at home before traveling?
It is impermissible to combine and shorten prayers at home before traveling because a person is called a traveler once he/she departs the borders of his/her country, and offering prayer that way was originally intended to exempt a traveler. And Allah Knows Best.