They really should've kept using "I" instead of "We" or maybe made it italicized and explain it's the royal "I". Similar to their explanation of "cheap sister". Like when you read a japanese manga and they use "Ore/Boku" instead of the watashi form "I".
When I was reading this before the comments, I kept thinking he's a bit cuckoo, and sees/feels his mother is still there beside him.
Also...I'm unsure how I feel. I find the Emperor a precious cinnamon roll...not sure I want him falling for his adopted mother in another body. I'm hoping this is some ploy by them to out the sister.