It was without doubt that some of the commanders wanted to oppose the Crown Prince's decision.
First and foremost, the Percival brothers just appeared sans any prior warnings. Aside from Marquiss Cynan, Count Morholt, and Hayyoth, none of them had knowledge as to what the identity of the two might be.
Second, more than being threatened that their position would be taken, the commanders questioned the Percival brothers' ability, albeit merely in their minds. In their eyes, the siblings were too young to be promoted as commanders within the Crown Prince's army. It was not a rank that anyone could just embody.