Looking at the point of view of a Somulian, whatever situation the Royal Family members were in could be dealt with easily compared to what was happening in the Military District. For one thing, lost technology was involved in the latter's situation, and in Somuli, it was something that no one could decipher or destroy.
Aran would know this, and so would his aides. Thus, if he wanted to seek reinforcements as soon as possible, the only people he could go to were the Royal Family members.
Yes, Aran ordered them to round up their forces and attack the fort Achim and his forces occupied. But he knew the elders of his family would always hold back their manpower and might even hide their powerful members. If, for argument's sake, the elders had truly listened to him and dispatched all their forces, were they— the elders, themselves— not considered reinforcements?
The answer was simple: they are considered reinforcements.