Your grandfather's uncle is your great great uncle. Your grandfather's brother would be your great uncle
There is no genealogical relationship. He is just your son-in-law's brother.
In relation to yourself, the brother of your maternal parent is known as your maternal uncle.
fourth cousin
3rd cousin I think:-)
cousin
Your grandfathers brother to you is your Great Uncle!
3rd cousin
Your grandfather's brother is your great uncle.
Your great great grandfather.
No relation
You would be second cousins.
Most likely they would not be related to you
He would be your great great uncle, but you could call him whatever endearing name you both prefer. my great grandfathers brother or my great uncle
Brother in law
Brother-in-law
brother