Make use of the verb ghuD "be in common, be co-" (admittedly clumsy definitions). It's used in constructions such as HoDpu' ghuD (literally something like "in-common captains," but a better translation would be "co-captains" or "fellow captains"). One could also say ghuD HoDpu' (literally "the captains are in common" but it really means they share the same status and, perhaps, work together). ghojwI' ghuD would be "a fellow student." puqpu' ghuD might refer to children who are growing up together (whether related or not).