As has already been mentioned, Wang Yu had both the ability and good reasons to help Chen Cheng escape legal sanctions, but he still personally arrested Chen Cheng. Therefore, the Qin Father and Son would not doubt the truthfulness of what Wang Yu said.
The reason for their furrowed brows was that neither of them could offer Wang Yu any assurances.
Qin Yuanzhu's purpose for coming to Bird City was out of concern for Wang Yu's whereabouts, to see where Wang Yu was injured. His arrival was a personal act, unrelated to this case, and naturally, he couldn't provide Wang Yu with any assurances.
As for Qin Guodong, although he was the Minister of the Security Department and was dispatched to Bird City on the orders of Deputy Leader Song, he actually did not have the authority to handle this case. The case would eventually be handed over to the Military Division, so he also dared not offer Wang Yu any assurance.