Is it permissible for my brother, whom I had suckled, to conclude a marriage contract between his daughter and my son?

Such marriage is impermissible since one`s nephew in this situation is considered an uncle to one`s daughter; consequently, he is the brother of her father by suckling. In such cases, the people in question should go to court to prove the suckling.

What is the ruling on someone who vowed to fast for two consecutive months, but failed to do so?

He is obliged to fulfill his vow by fasting for two consecutive months, but if he fails to do so then, it remains a debt on him until he either fulfills his vow, or dies. In case of his death, his guardian is supposed to fast on his behalf, or donate food from his estate in return for fasting, but if the guardian fails to do so then, it is all in the Hands of Allah.

Is it permissible to make up for missed fast after the beginning of the second half of the month of Sha`ban(the month before Ramadhaan) ?

Yes, it is permissible, but one who had missed fasts should hasten to make up for them. As for the Hadith mentioned in this regard, the prohibition is for offering absolute voluntary fasting.

A man cursed Allah, is he allowed to perform prayer without making Ghusl?