After all, Hugo's solo combat ability was extremely strong; he was one of the only two super soldiers with a straightforward combat style, the other one being Sky Shadow.
As for Angelina, being a Mental Ability User, one couldn't let their guard down against her psychic attacks, which could catch you off guard and cause a second of distraction that could be fatal.
As for the Haier brothers, honestly, they were the ones Xia Mu was most wary of. They shared thoughts and intentions as seamlessly as twin flowers, which has scientific explanations. However, groups like theirs often have congenital defects, but the Haier Brothers were different. Growing up in the Charles family was a result of their bloodline that had been passed down through generations. Just like the concept of 1+1, if such a combination had no flaws, the effectiveness they would bring to combat was unpredictable.