The Rong family needs a serious cleanup. Toxic grandma. Ruthless and cunning blind sister. Yun xi is cunning but knows when to stop. The other sister is always creating trouble without thinking. Grandma is passing her toxic brain to the children. With no parents around she's been controlling the sisters. The way Bai Luo was looking at the blind sister when she was with grandma is like he's noticed something off with her. Luckily cousin warned her that someone within the family is after her of which ML already hinted it.
I think like, He Xing Ming was a cruel and calculating person, with little to no remorse. But from what is seen…
I think you didn't see the part where he told her that she seems cold from outside but inside she is soft unlike the blind sister who is cruthless. He knows what type of a person she is. The problem is their lack of communication and trust and the fact that her grandmother is kinda controlling it wouldn't be a surprise to find later that the man she claimed to be FL grandpa is fake and that so called vow.