Switching party members isn't possible by default, but VX Ace has a lot of scripts, so it's likely possible with one of them. It would be a pretty substantial balance change, though.
As for the logical justification, you should assume that all party members are fighting at all times, you just only control one group. That's why they all get EXP and why there's a threat to more than the front line. I actually made this explicit during the Third Arclentian War: there's a segment where there are ogres that your non-party members are fighting while you fight a different boss battle.
As for the logical justification, you should assume that all party members are fighting at all times, you just only control one group. That's why they all get EXP and why there's a threat to more than the front line. I actually made this explicit during the Third Arclentian War: there's a segment where there are ogres that your non-party members are fighting while you fight a different boss battle.