
Chapters 3 is not ok
I get her family was trash so it's better to get away from them.
But she obviously loved her family, she prayed everyday for their well being.
Even if her older sister got mad at not being the saintess, the logic reaction of the younger sister would be to cry and beg the prince to not put her family in jail.
Her family she loved so much is going to jail and she is happily smiling at the prince judging them, no way.

I’m not so sure about that. The impression I had was totally different when taking the context into account.
She was being abused—mentally, emotionally, and even physically to a degree—and was basically brainwashed into thinking her sister always worked hard for the sake of the kingdom and that her sister (and parents) deserved to be happy while she wasn’t because of her “uselessness.” So, inevitably, in her manipulated state of mind, she would pray that her family would get all the things they deserved. And, of course, they did but not in the way she had imagined it.
Still, I agree that her reaction was a little odd. Regardless of whether she was brainwashed or she legitimately loved her family, there should have been some kind of pushback or pleading for the situation to change. Since these are one-shots, I know that some plot won’t be able to come through as well and things are forced to be left out due to time constraints among other issues, which I think happened in chapter 3.
This is an oneshot with a missing extra
(Extra spoilers: they keep having sex and eventually live together)