Complex sentence: This specifies inter alia "5 years of seniority in the Order and 2 years of seniority of military service", in other words 5 years belonging to the Order, and 2 years military service.
Split into simpler sentences: This specifies inter alia "5 years of seniority in the Order and 2 years of seniority of military service". In other words 5 years in belonging to the Order, and 2 years military service.