Actually, when they were standing outside the hall, they had heard what Lu Fenying said to the ministers.
Whether it was his question to the master of the Su family or firing back at the emperor, they carried the same meaning: If he truly had no choice, he would reveal the fact that Qian'er had Dragon Spirit Blood.
People with Dragon Spirit Blood were hard to come by. Forget one city, ten cities would be worth the bare minimum.
Lu Fenying had openly taken Qian'er out of the residence to make Gu Bailu and Feng Qingtian nervous and follow him to the palace.
He had deliberately said those words for them to hear so that they would help him.
If he really wanted to reveal Qian'er's identity, he would've said it directly instead of speaking so much nonsense.
Although Gu Bailu and Feng Qingtian knew what he was plotting, they had no choice but to go along with it.