niephew

Gender neutral term to refer to the relationship of a sibling's child (niece or nepew). The word is a portmanteau of niece + nephew

My brother's five children (of various genders) are collectively my niephews

Aunkle

(alternatively "Ankle") a gender neutral term for a person bearing a relationship of being the sibling of the person's parent. Aunkle is a portmanteau of aunt + uncle.

Greg's father has 3 brothers, and 2 sisters. Greg has 5 aunkles on his father's side