Your parent's cousins are aunts and uncles only if they have brothers or sisters who have children. Your parent's cousins are your cousins, once removed.
They could be your parents. Or they could be your aunt and uncle. The other alternative is that they are not related to you at all.
The cousins of your in-laws are not related to you and neither are their parents. However, the parents of your spouse's first cousins are your spouse's aunts and uncles, and thus your children's great aunts and great uncles.
Cousin. Your parents brothers and sisters are aunts and uncles. and the aunt and uncles children are your cousins.
their parents, brothers, sisters, cousins, aunts, uncles, and people who are related to them.
Your aunts and uncles are the sisters and brothers of your parents.
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]
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]
Cousins are the children of of both your parent's siblings (your aunts or uncles.)
Extended family habitation
People who are related to you: parents, brothers, sisters, cousins, uncles, aunts, grandparents, etc.
aunts, cousins, daughters, sons, and friend.
Perhaps you mean "cousins", children of your uncles and aunts.
The grandchildren would be the parents, aunts and uncles, and first cousins once removed, of the great grandchildren.