It's amazing to see every your dialog system getting used for new purposes! I hope it turns out to be a great asset for this assignment.
On the part that your characters might be lacking a bit of emotion given that they're not using dynamic sprites there could be some easy work arounds for this that would work as affordances other than pure text. For example you could put a blue filter or multiple the sprite image to blue to convey sadness, or you could have the image translate and rotate slightly to show excitement. Other aspects are little exclamation marks, question marks, dots, etc appearing on the sprite. This way assets can be modular instead of singularly built into each one.
I'm looking forward to seeing further progress on your game!