I explained to you but you still ask the same question while you firmly believe your own assumption. Then why ask others and call them stupid and rude? Strange!
I don’t think he killed his friend. He just used his name.
You would need to kill a person if you want your identity changed to his. He wasn't just changing his name but he was stealing another person's identity. When chairman kang investigated about his past, had he not killed the real doha his identity would have been found out.
Cho sunghoon (now known as choi doha) grandfather is not chairman kang. His grandfather is the guy who died in the car accident. Real choi doha's grandfather is the old man we see at the hospital. Chairman kang is not grandfather of any people we saw with him. And you are right about your first question.
And you are right about your first question.