Yuhon is too impulsive. Should have talk about things with his wife before going on killin...

But, it's not proved yet that he is the killer....but if your opinion is true...OMG....kusanagi mizuho sensei making it complicated

This impulsive side of him is what made Yona say that he was not fit to be king when she talked to Soo won about the conflict with Shin or what country ( sorry I am bad with name memorizing). The one with the five stars. And I totally aggre with Yona especially if he killed Kashi and wanted to kill Yona as well with her that time. Like do you have a reason asside a rumor? You that greedy even tought you said you only wanted to protect your family and happines? That the slightest possibility of you being sidelined because of king hiryu s reincarnation ticked you to murder? Of course only if it is true what we speculate. But I can imagine it pretty much. Also Kashi probably did not bring Yona because she saw her future of being killed.
╥﹏╥ and if Il got to know that his own brother killed his wife then him killing his brother is also reasonably understandable and would explain the story. As well as Soo won s intention to become king. If he was not told that his father killed Kashi then he would not understand the reason his father was killed and would want to avenge his unjust death.#－.－)
But this is just my speculation.

Or maybe soo won wanted to free yona from king il.... We all know how passionate king ill towards hiryuu or anything similar to crimson dragon. And wht about soo won like yona too? If kashi can saw a future then she must know that soo won is the cause of yona sengsara

Miserable not sengsara