When Arad and Zephyr reached the entrance to the royal quarter, they had to stop their night quest. The door, windows, vents, even the floor itself. Everything is enchanted with several spells that detect intruders and immediately alarm the whole castle. No one can even enter or leave the quarter without a royal imprint, and even when they do, that entrance is announced to the castle guards.
Even if Arad were to bring Tyal in, her entrance would be announced, and the guards would know that something is off. She is supposed to be asleep in the guest room with Arad.
This level of security made Arad aware of two things. He should make the security in his castle better, and if he is to find anything useful, it must be kept in Gale's royal quarter, away from everyone's prying eyes.
Arad and Zephyr retreated to the guest room before anyone could notice their absence... well, no one would ever have the chance. There should be only one Arad, and they don't even know that Zephyr is here.
