What is the explanation of the two verses of kalalah in Surat An-Nisa, and are they abrogating and abrogated or complementary to each other? And if a man dies with no children and his sister inherits half, where does the other half go, and do the children of the deceased brother inherit their father's share?

There is no contradiction or abrogation between the two verses of kalalah. The first speaks of uterine brothers and sisters, while the second speaks of full or paternal siblings. If the deceased leaves a full or paternal sister and sons of a full or paternal brother, the sister inherits half, and the remainder goes to the brother's sons. If, however, the sister is uterine, she inherits one-sixth, and the remainder goes to her brother's sons. If the deceased leaves no heir other than his sister, she takes the entire estate by fard (prescribed share) and radd (return).