These talks need to be about 1 thing only-destroying North Korea’s nuclear weapons program. All the frilly stuff can be handled later.
Moon is a dedicated socialist and a believer in the Juche cult; they worships the Kims as gods. It is the subject.
If unification takes place it will be under Kim; Moon will be his puppet. Korea will then become a closed state under Kim rule; Japan will begin a major military build up and acquire nuclear weapons.