They are your cousins.
Cousins are the children of of both your parent's siblings (your aunts or uncles.)
No, "uncles" does not have an apostrophe. An apostrophe is used to indicate possession or to form contractions, but in the case of "uncles," it is simply a plural noun.
Cousin. Your parents brothers and sisters are aunts and uncles. and the aunt and uncles children are your cousins.
aunties and uncles
cousin
Extended family habitation
Your grandfather's children are either your parents or aunts or uncles.
Perhaps you mean "cousins", children of your uncles and aunts.
Your aunt is your child's Great Aunt, so your child is her great niece or great nephew.
I believe they would be great aunts or great uncles.
Your brother or sister are your siblings. Your cousins are the children of your aunts and uncles.
great great (etc.) grandparents great grandparents grandparents + great uncles and great aunts parents + uncles and aunts [=parents' siblings] siblings + cousins [=uncles' and aunts' children] children + nephews and nieces [=siblings' children] grandchildren great gandchildren great great (etc.) grandhildren also cousins and second cousins [=(great-)grandparents' descendants]