Reimian Empire

I still don't quite understand what we're supposed to get if we succeed. We already have all the stones.

Perhaps some of them are fake and not suitable for solving the puzzle. Perhaps all the activated chairs will open doors for us. In any case, there are four puzzles, and I don't think that any two of them will be enough. Perhaps additional slots or statues will open up for new stones.
And if we're talking about choosing which character to sacrifice, my priority list is: Tsukiko > Ayano > Livia > Celiad = Tria > NPCs. This is in terms of who we should LOSE from the characters. This is my tier list of champions for this quest. Celiad and Tria are not very high on the list because I haven't seen them perform exceptionally well yet, but I don't rule out that it's just that there hasn't been a suitable opportunity. Ayano also hasn't been performing well, but logic suggests that she's somewhere closer to the top for this location.
I would really like to keep Castor until the end, both for role-playing reasons and for the quest. I think that if we somehow manage to get out and return without him, we'll be put in the stocks and executed. It's better to think of him as a fairy-like advisor from Zelda.