Glad you enjoyed the Grace path! :B
There’s no way to know for sure who is doing the quotes between chapters, that’s part of the larger mystery of the game and will be explored more in future dlc. But there are enough subtle hints that you could make a good guess - lots of players on discord have been trying to figure these mysteries out.
The finished Grace pics with shading should be available soonish, there are just a few more pictures to finalize, the update will be available to everyone who owns the game.