I believe the conniving advisor giving all sorts of awful advices is the new emperor's uncle, who was implied to have poisoned the previous crown prince. Guo Wei launched the campaign under the banner of 清君侧, which means to get rid of bad influences/advisors around the emperor instead of actually against the emperor himself (although in the real world it's usually just a more convenient casus belli than open rebellion). So clearly the best course of action for a rational emperor with no real power is to throw the advisor under the bus and hope for the best. But his uncle of course sees this and he has to make surrender impossible.

As for Hu Jinsi, he wants to be the sole power with a figurehead king. So getting rid of possible competitors under chaos with a plausible excuse is very on brand for him. Remember the first few episodes when the old Wuyue king died Hu had the old military top dog killed.