The FF6 party-forming system can be done pretty easily with eventing. The process would look something like this:
1. Memorize hero location
2. Teleport hero to a custom map that is meant only for party formation
3. Using Key Input processing, allow a cursor to move around a grid and select characters and move them to the active party box.
4. When done, determine which characters are in the active party box
5. Remove all characters from the party
6. Add the characters in the active party box back to the party
This is why I wanted to know the intended design purpose--because as suspected, the position in the party doesn't matter at all to achieve the goal of swapping characters in and out like FF6.
EDIT: I have created a demo doing what I just described above. It can be found
here.