Your uncle is either of your parent's brother.
your uncle is your sons great uncle
The English language recognizes no relationship between you and your husband's great uncle.
Your grandfather's uncle is your great uncle.
Your uncle's son is your (first) cousin.
Your Great Uncle is your the brother of one of your grandparents, and therefore the uncle of one of your parents.
Your granddaughters and son have the relationship of nieces and uncle. Your granddaughters being his nieces and your son being their uncle.
His great uncle
Your great uncle's daughter would be your aunt.
Your father's brother is your uncle. You are his niece (if you are female) or his nephew (if you are male).
You are your uncle's niece. You and your uncle's children are first cousins to each other.
He is your nephew, and you are his uncle.
He is your nephew and you are his uncle.