
That's how Ariadne was fooled. If this is the intention of the artist (to show how someone could be fooled by a manipulative abusive cheating bastard) then they did well.

Like I'm currently rereading and in Chapter 36 there's a letter from a young lady saying 'your passion of waiting outside of my window frame all night until the morning dew falls has mysteriously vanished' really tells that Cesare only behaves like that when he hasn't gotten the lady's heart yet. If he had gotten what he wanted, he left them to find another 'quest' to be conquered. Remember that Cesare wanted to have Isabella's heart too until he found out about her flaws and Ariadne entered the picture.

Zeno sealed Jae-ha, Kija, and Shin-ah not because it's the end of their lifespan. That chalice is really important to Zeno not just because it's what gave them the powers, but it can actually extend their lifespan. There are a few theory I consider about this,
1. Zeno sealed the dragons so they can recover, both their souls and their bodies.
2. Three of the four dragons aren't going to die young this time around because the reincarnation of King Hiryuu has descended. The first generation of the dragons all lived until old age, the descendants died because King Hiryuu wasn't in their generation(s).
3. Zeno would release them back when they're ready or when the time has come for their release.
4. As Kija felt, Jae-ha and Shin-ah are still alive, it made no sense that the three dragons are dead or waiting to be reincarnated again because Yona would sense it. Zeno looked relieved because he sealed them before they died or lost themselves.
Again, this is just my theory. I hope it's not too far off.

Disclaimer ofc this is just what I got from the ending, it was rushed, but still can be explained, assuming that the author didn't plan the ending to be like that (as in the sisters), these are the possible explanations :
1. Lisha was hidden from birth (doesn't really make sense but hear me out) because of their mother's family's pressure, one of them would definitely become an experimental subject, Lisha was chosen because of her ability.
2. Libertia and Alisha are twin sisters, but when Libertia sent Lisha to another dimension, only she could remember about her twin sister, the others had their memories tweaked because of some side effects of sending someone to another dimension or Libertia was the one who erased their memories about Lisha. When Lisha woke up and Libertia's soul was already gone, her hair color changed because Lisha's soul had 'sync'ed with Libertia's body.
Everyone was probably confused about her hair color, but they were more focused in Lisha. When Lisha woke up, the people's memories about Lisha was unlocked, it's as if Lisha was living quietly in the palace or in her maternal family's house, then Lisha explained to her closest friends and family that she's actually in her sister's body (or the full story)
3. There might be translation mistakes with the name (or the author made a mistake) Lisha is the name that Libertia used to name her puppy, I assume that she was actually talking about her twin sister's nickname instead of hers, so the 'Beauties' had always been calling her 'Lisha' instead of 'Litia'
I have read the LN like years ago and waited almost everyday for the manhwa adaptation, yet somehow only knew about this now??? They are so gorgeous and the art didn't disappoint at all