Accompanying the grandchildren of one's sister for Hajj

Question:

Does a man have the right to accompany the grandchildren of his sister for Hajj?

Answer: 

The grandchildren of the sister of a man are the children of his nephew or niece. The niece of a person is Mahram. Similarly, the child of the niece is Mahram. Therefore, a person has the right to accompany the grandchildren of his sister for Hajj.

[English version of "Accompagne sœur so ti zenfants dans hajj" – Al Jamiat – Vol.3 No.10]