If Sam is John's son, and David is Sam's uncle, does that make John and David brothers? Additionally, if David has a sister named Sarah, what is Sarah's relationship to Sam?

Provide a very brief response.
If David is Sam's uncle, and we know that Sam is John's son, it follows that David must be John's brother because uncles are typically the brothers of one's father or mother. Therefore, John and David are indeed brothers.

Regarding David's sister Sarah, since David is the brother of John and John is Sam's father, this makes Sarah the sister of John as well. Therefore, Sarah is Sam's aunt because aunts are typically the sisters of one's father or mother.