But you can already just select one character out of the party and position him here and there as you wish. So sorry if I'm confused but you are already saying you want things, that are already possible in game. Idk if my game is just bugged correctly, but when I put one character into sneak mode, only he ever moves and the rest of the party stands by for orders. So one by one, outside of where I'm planning my ambush, I select a character, enter sneak mode, move to position, and then select next character. One two three four, enter battle.
What in that process are you wanting to make more RTS like? When you say RTS I'm thinking like Total war and Starcraft, so maybe we're on different pages.