1. why didn't the ghost kill jaime, owen, charlotte and dominic who lived at the manor? why only kill rebecca, peter and hannah?
2. the viola ghost had physical abilities but the peter, rachel and hannah ghosts did not. we see hannah can't eat but she can open doors.
3. who was the guy talking to henry at the office?
4. why did dani see peter's ghost right away. owen and jaime did not?
It's been a minute since I've watched but from the top of my head:
1. Viola only killed things in her path during her walk. The walk may not have happened every single night, but it's a looming threat which is why Dani is warned to stay in her room. Viola didn't kill Hannah, and I don't know who Rachel is.
2. It's unclear, but the story already has us accept that Viola is unnaturally strong (her rage? her psychological disposition? etc.). Viola's curse binds dead souls to Bly, so her ability to kill/interact is not the only thing that she can do differently.
3. I presumed that was just Henry talking to himself. I don't think it was anything supernatural.
4. Are you talking about when Peter was chilling in the distance at the house? I presume it was just luck. No deeper meaning.
Rebecca not Rachel. Sorry.
You are right - Hannah was not killed by Viola.
Yes. Dani sees Peter as soon as she arrives.
Oh yeah, Peter Quint kills Rebecca.
Yeah, I think only Dani seeing Peter in the distance wasn't anything special there. It was just her happening to be the only one who noticed.