
Same... the plot revolves around Charlotte and her disciples, that is what the author said, there are 5 disciples and they are all important, she sees everyone as problematic children, they need to let go of the nest and stop depending on
her, if she will stay with a disciples is like continuing to be tied to them and especially the youngest, he always depended on her, he needs to make his own way, also I doubt that Charlotte will stay with Calamity knowing that he killed / possessed the body of one of her disciples

Didn't really killed him, in fact if you piece the clues throughout the whole manhwa, Evan and "Calamity" you spoke of are in fact the same person, it's just that Evan was created after the "Calamity" was defeated by Charlotte, and didn't have memories of his past. After Charlotte died, he recovered his memories when he died as Evan once, so Evan is "Calamity" from the very beginning. It was also implied that Charlotte knew everything about him as Evan told her that she knew when Charlotte was talking to him in the form of a cat. There's also a phrase where Charlotte talk about saving Evan when he was first accepted as her disciple in some of the chapters, I've forgot what ch it is but you could look it up. I hope this clears it up.

She wants to save him currently because he is her disciple, in the past she did not kill him because he was an innocent child, however the fairy king always tells her that she is going to regret it even tells her that now she has the same options as the past (kill or be killed), in chapter 51 it is implied that he is the main cause of the curse of charlotte (I do not know what her curse is about and to date the manhwa does not mention it) it is true that calamity is with Evan but They not are the same person, Charlotte knows how to identify him by the color of his eyes, she is friendly with Evan but when his eyes turn red she is more agressive because she knows him is not evan, it is said that Evan died, Evan mentions that he had already died, she believes that calamity killed him or possess his body, evan says that charlotte knew it but he means that she knew there was something wrong with him and that is why she wanted to get rid of him, charlotte thinks that there is a disaster in his body, she does not think that calamity and evan is the same person

Wait wait wait, are we pertaining to "Calamity" here as the Demon King on the first chapter?, if so Evan is really the same with "Calamity". His eyes are naturally red, it's a unique features of a demon, in which Evan is. It is probably the quality of translation so some words may cause misunderstandings or misinterpretations but, I didn't see Charlotte wanting to kill him, in fact, she is trying to save him, same as when he was still a child and now. Charlotte already said it herself in her cat form, the person who wants to kill Evan is her first disciple, the Emperor of Marveil as he was the root cause of everything, i.e, "Calamity".

It has never been mentioned in the manhwa that calamity (which is really his "name") is a king, I don't remember why we all refer to him as demon king, in other translations they call him "calamity, disaster, cataclysm", charlotte doesnt wants to kill Evan, the fairy king gave those two options to charlotte in the past (charlotte has shown that she would not kill innocent beings, examples like Dan Monte (Dan's mother wanted charlotte to kill Dan, but she didn't, she saved Dan and raised him) the fairy king tells her the same thing when he gives her the blessing "you have the same options", of course charlotte doesn't want to kill him, she wants to find a solution however Evan doesn't want to say anything, in jail even though she asked him to speak, He didn't say anything, The Koreans already said that both Evan and calamity are not the same person, they are both different, calamity is possessing / using Evan's body, he appears when Evan's eyes turn red, Evan's eye color is gray, yes , carsilion wants to get rid of Evan because he is the cause of the disaster (Evan's Korean fans hate to carsilion a lot for this, however I think that is what an emperor would do, get rid of the main cause of the disaster even now they call to Jeffrey a villain because according to them he wants to "get rid" of Evan which is wrong because he has not done anything to him, it is ironic because they dont say anything when Evan was on the side of the bad guys, when he was helping to kidnap people and when despite he mee to yurian, he let them use her, for his fans he is a saint who has not done anything, only the other characters are villains), if nobody kills him, the same thing that happened 100 years ago with Calamity will happen, charlotte wants to give him Another chance (chapter 56, she says that it is the last hand she extends to him, therefore if Evan does something bad again she will no longer help him) therefore she took him out of Marveil, charlotte does not want let his disciples kill each other

Ohh, Demon King was some sort of title, anyway, I don't really know if he is one but I just refer to him as one because demons always respect strength, and that title usually goes to the strongest person in their clan, in which he is. It's like how you call your older neighbors' as auntie or uncle, even though you're not related, it's something like that.
If she end up with one of the diciple im dropping.