Is the marriage contract considered valid if concluded at home by the marriage official (Ma`zon)?
Yes, it is valid as long as it is registered at the court.
What should a person, who delayed making up missed fasts of last Ramadan due to the continuance of the same excuse, do?
It is permissible for one, whose excuse for not making up missed fasts of last Ramadhaan has continued, to delay fasting until the excuse ceases to exist, and he is considered neither sinful, nor obligated to pay a ransom. And Allah Knows Best.
Is the two Raka's after Friday Prayer an act of Sunna?
Performing Two prostrations after the call of Friday's Athan is an act of Sunna, since Al-Bukhari stated in his Sahih: (The chapter of praying before and after Friday's prayer). This indicates that he mentions Friday's prayer exactly as the Duhr prayer (Afternoon prayer) as regards praying before and after the call of Athan. And Allah Knows Best.
Is a wife considered sinful if she asked for divorce because her husband married another woman?
A second marriage is lawful, and so it is impermissible for you to ask for divorce because of that. If you are certain that you won`t be able to deliver Allah`s rights and those of your husband`s , then it is permissible for you to ask for Khul`a (Divorce on the demand of the wife). However, you should exercise patience since after difficulties, there is easiness by the will of Allah.