One of the reasons that you probably haven’t gotten any replies is because your post is very hard to understand.
You need to be more specific about what you are trying to accomplish and whether the “user” for the domains is the same or different. You mention VPS at one point which implies the others are on shared? Or is it all on the same VPS?
In any case, using specific domains and sub-domains is fine in the forum, and you will probably get better answers explaining it that way than trying to do what’s above and overly generic.