Alexander's plan to make the captured nobles cooperate was simple- threatening to not recognize them as nobility but as instead common peasants who could then be killed or sold as common slaves.
"You have no one to come save you. You are alone here. No one knows whether you are even alive! I can do whatever I want to you," Alexander's threat was naked and real as he laid bare the situation to the defeated men.
To this of course the esteemed men had protested at first, one pointing at Alexander and very simply angrily shouting,
"Lies! His Eminence Manuk would never do that. He is probably caught up in some urgent matter and will no doubt soon contact you."
While another of his friends too quickly chimed in,
"That's right! And even if Lord Manuk were to encounter something untoward, there is still our own lord. He will surely send messengers to inquire about us! Our families will never let us be forgotten."