Your great great great uncle is the brother of one of your great great grandparents.
Your great great great uncle's son is the first cousin of you great grandparents, so he is your first cousin, three times removed.
your cousin
It means you have (or had) at least two uncles and at least two great-uncles, and that is all it means.
great uncle
Your great grandparents brothers and sisters are your great uncles and great aunts.
His great uncle
your uncles daughter would be your cousin
Your nephew's son is your great nephew.
Great aunty
great nephew
Your husband is great uncle to your niece's son (your great nephew).
You would be a great uncle, so they would be your great nephew
Your daughter's daughter's son is your great grandson, and you are his great grandfather or great grandmother.