I doubt everyone knows. It makes sense for Robia and Nadricka to know since they almost always have been with her or around her ever since she transmigrated into that body, but the others haven’t been around enough. They definitely need more screen/panel time.
Not everyone everyone, I meant everyone in her harem and by that I was pointing out Nadricka, Robia and Eclot because I remember in one of her chapters, Eclot was really surprised by her action, can't recall exactly what it was at this moment though. Even if the people around her don't suspect she was someone else who had transmigrated into the princess' body, they probably do suspect something is wrong because her character just did a 180. She didn't just gradually change.
We completely saw this coming, didn't we. I mean, like how would people not notice, she's completely different in character from the original princess. I think probably everyone in her harem knows, not too sure about Ettsen though, I have serious doubts about his mental capabilities at this point.