Is it permissible for the father to give the Zakat of his money to his poor married son?
It is permissible for the father to give part of the Zakat to his poor son, if the latter was sound and healthy, because in this case the father isn't obliged to spend on his young son, even though; he is considered one of the Muslims poor. And Allah Knows Best.
Is it permissible for me to make up for my late father`s missed fasts? and should I make an intention to this end by saying: "I intend to make up for my late father`s missed fasts?
It is permissible to fast on behalf of the deceased father in order to make up for his missed fasts, and you should make the intention for offering fast from night time, but uttering the intention isn`t a condition. And Allah Knows Best.
Is it permissible for a person who has to make up for missed fasts to fast six days of Shawwal (the month directly after Ramadan) before making up for the missed fasts?
Yes, it is permissible for him/her to do so, but it is better that they make up for missed fasts first. And Allah Knows Best.
What is the ruling of Sharia on using IUD (Intrauterine device) temporarily and by mutual agreement of husband and wife?
All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
There is nothing wrong with this if this device is used on temporary basis and by mutual agreement of husband and wife since this issue falls into family planning, which is allowed by Sharia. However, this is provided that the device is inserted by a female doctor and that it doesn`t cause harm to the woman. And Allah The Almighty Knows Best.