[quote=Sketcher]
Everyone in the same clan would know one another, right?
[/quote]

Because Naruto totally knew Nagato beforehand. Yet they descend from the same clan. 
I guess it depends on the backstory? Because ya' know, if the clan is divided or some have been on their own for a long time, would make sense that they're strangers to clansmen who never met them before they've left.