Your Aunt is your children's Great Aunt.
Your brother's wife is your children's aunt as long as they are married. If they get divorced, she is no longer any relation to them.
your grandma
Uncle if you are male and aunt if you are female.
If she's not your mother, that would make her your Aunt.
She could be your grandmother. Or she could be your great aunt.
Your great aunt's daughter's children (her grandchildren) are your second cousins.
aunt or uncle;) depends on the gender
You are their aunt or uncle and they are your niece or nephew.
Your parents are great aunt and great uncle to the children of your first cousin.
Your neice's children are your grandneices and grandnephews. You are their great aunt or great uncle.
Your brother's wife is your children's aunt as long as they are married. If they get divorced, she is no longer any relation to them.
Your uncle-by-marriage's nephews might be you and your siblings. You are your uncle's nephew or niece.They might be the children of your aunt's siblings (your aunt being his wife), in which case they are your cousins.If they are your uncle's nephews by virtue of being children of his siblings, they are no relation to you at all.
Aunt in-law
Your aunt is your daughter's great aunt. Your daughter is your aunt's great niece.
Your great grandmother's children's children are her grandchildren. They could be any of the following:your grandparentyour second cousin twice removedyour great aunt or great uncle
Your Aunt's first cousin may be your second cousin, onve removed or may be no relation to you at all.
You granddaughter is a great great niece of your aunt. Your aunt is your granddaughter's great great aunt.