Yesss. He actually doesn't care for her. He is only keeping her alive for this. Since she's his sister he thought tht maybe sacrificing her despite not having any special feeling for her will work. But slowly he started to care for her for real so i have no idea whether he will sacrifice her or not. Also may i know where did u read it? Cause the place where i read it stopped translating the novel.
You can read it from here!!
https://wuxiaworld.site/novel/the-precious-sister-of-the-villainous-grand-duke/ ヾ(❀╹◡╹)ノ~
I really can't remember well but the last time
I read the novel in that chapter for her brother to succeed (I don't know i really can't remember the term but it's like to be officially part of the successor or to succeed the so called competition within the family) he needs to sacrifice something important to him or is special to him to be able to.succeed and he says that somehow he will sacrifice his sister.
But i don't know if he really gonna do it, cause I've stop reading the novel cause it has slow updates, i hope for a Happy ending