Because of their advanced degrees, medical doctors are commissioned as Captains in the US Army. Megan, Teddy and a few others wear the rank insignia of 1st Lieutenants.
Family members, (siblings, parents & children and spouses), are never stationed in the same unit, the same area or the same theater of operation during wartime or in combat zone, therefore Owen and Megan would not have been serving in the same unit in a forward area and only one of them would have been deployed to the region.