When Julia and Benia were beating up the Eredar Twins, they didn't think too much about it and just wanted to vent their anger. But when Kil'jaeden's guards were ordered to capture them, they immediately realized that something was wrong.
In particular, Benia was a succubus. When she was in the world of Ashan, she had seen the schemes and conspiracies between demons, so she immediately realized that the provocation of the Eredar Twins was premeditated. Their goal was most likely to target Roy, who was behind them. In this case, they naturally couldn't show weakness, so she immediately communicated with Julia and killed Kil'jaeden's guards.
Even though they beat up the Eredar Twins fiercely, Julia and Benia were still very restrained and knew their limits. But now that they began to fight without holding back, the situation was different.