When you go to the database (in the editor, not the scripts) in the first tab you can see the actors list. Each actor has a certain id. These actors are stored in $data_actors, and then in $game_actors.
You can use the systaxes in the Call script command (tab 3 of the events command list)
$game_actors[XXX].not_available = BOOL
XXX must be replaced with the ID, without the leading zero's
BOOL must be replaced with true or false.
so, what happens if we do:
$game_actors[1].must_be_in_party = true
Now, Arshes/Axulus (id = 1) MUST be in the party. You can not switch him to the reserved list.
$game_actors[2].not_available = true
Now, Basil (id = 2) can NOT be in the party. You can not switch him to the party list.
$game_actors[7].disabled_for_party = true
Now, Gloria (id = 7) will not show up in both the party list and both the reserverd list.
$game_actors[1].must_be_in_party = false
$game_actors[2].disabled_for_party = false
$game_actors[7].not_available = false
Now, Arshes can be in the reserved list again, Basil can be in the party again, and Gloria will show up in the list again.
I Hope you understand.