He died and left behind a wife and nephews and nieces

Praise be to Allah.

If a man dies and leaves behind a wife and nephews and nieces, and there are no other heirs apart from these, then the wife gets one-quarter because there are no children. The sons of his brothers get the rest by virtue of being male relatives on the father’s side, and it should be divided equally among them. The sons of his sister and the daughters of his brothers do not get anything, because they are not among the male relatives on the father’s side.  

Allaah says concerning the inheritance of wives (interpretation of the meaning): 

“In that which you leave, their (your wives) share is a fourth if you leave no child”

[al-Nisa’ 4:12]

And the Prophet (peace and blessings of Allaah be upon him) said:  “Give the shares of inheritance to those who are entitled to them, and whatever is left goes to the closest male relative.” Narrated by al-Bukhaari (6732) and Muslim (1615). This indicates that male relatives on the father’s side may be entitled to inheritance, and that the closer relatives take precedence over those who are more distantly related, and they inherit after the shares of inheritance have been allocated, if anything is left for them. 

What is meant by shares of inheritance is those that are stipulated such as one half or one quarter or one eighth. 

And Allaah knows best.