Their plan for those two men was for them to kill the wicked concubine if they had failed. However... didn't the Han Emperor already kill the wicked concubine on their behalf? So, how could the target suddenly change to the Emperor?!
If someone searched for the perpetrator, they planned to let those two men point at the eunuch who hired them to begin with. No matter who the eunuch's master was, they didn't care. It wasn't their business anyway to care about the power struggle inside the palace --- they just needed to get their revenge and leave the mess behind.
"Is this Feng Yong Rui's doing?" Yao Ling whispered softly at Yao Ying. However, why would he do that? He was so loyal to the Han Emperor, so it didn't make sense for him to do this.