A troubled young woman from a dysfunctional family drags her father into a world of incest and revenge after the murder of her mother and brother.

Correction: the daughter is the protagonist. But who is the antagonist?

Who is the protagonist? Who is the antagonist (that is, do they know who the killer is)?

I think the second one you just gave is a lot clearer.

Yes she has an incestuous relationship with her father.

Alternative,

'Following the tragic murder of a mother and son, a devastated father and daughter are thrown together in a violent orgy of incest and revenge.'

Is this a mystery or search for the truth story? It seems like that is where this logline is going, but it's not entirely clear.

Also, how does she drag her father into the world of incest? The way it is written, it almost seems like the heroine is having an incestuous relationship with her father, which I don't think is what you intend. If she is taking her father along with her while searching for the truth, that needs to be more clear. Otherwise, there might be some people who misunderstand what your story is about.