What relationship am I to my niece?
A nephew is the son of someones brother or sister. A niece is the daughter of the persons brother or sister. To the nephew or niece, the person is their uncle or aunt. The relationship of aunt/uncle to niece/nephew is an example of second-degree relatives, meaning that their coefficient of relationship is 25%.
What do you call a daughter of your cousin?
The child of your cousin is still your niece and nephew.
The direct descendants of any cousin are cousins once removed. thus, the direct child of your second cousins are second cousins once removed. . The grand children of your second cousins is your second cousins twice removed. and so on. In-laws refer to relatives related by marriage.