Do understand, that the Kim regime is dynastic, and has been in power since about 1950. That family enjoys nearly godlike status in North Korea, and loyalty to them runs generations deep..
It would likely be harder to depose them than you think.
Yep, It’s in the North Korean Constitution that only a direct descendant of the Kim family can rule.
Apparently, that is why the half-brother was assassinated - the Chinese were going to kill Kim Jong Un, to use the other guy as a more amenable puppet.