Responses
when IL confronted and killed his bro, the bro (Soowon's dad) said Yona's mom was bringing ruin to the country by feeding lies and religious fanaticism to IL and their father. He pretty much admitted to having her killed.
Also a couple chapters ago Yona confronted the scarface bodyguard of Soowon's about how he was the one that actually committed her mother's murder on Soowon's dad's orders.
It can be inferred at this point that Yona's mother was murdered by the scarface dude on dad/bro's orders.
honestly, I don't get why the author drops a new character, like why !!!? I hope it's not to make the story longer! and if that is the case, there are a lot of mysteries we still don't understand or know about for example, how yona's mother actually died, and I desperately want to know more bout hak's past and who are his real parents since his grandfather adopted him