Blumhouse pictures specialises in psychological horror, so their films are rooted in symbolism and metaphor. Sometimes they hit their mark, sometimes they miss... this one was just off the mark. The hit was literally in the first few minutes in and the last few minutes out, it lost itself and the audience in the middle... ironically, that's precisely what was happening to the family. They (the family) were all processing their grief individually; "they"(who came knocking) can be perceived as the children of grief.

There is an extra challenge with films of this genre in conveying intent, because it relies on major attention to detail in visual imagery and exceptional precision in the storytelling, which must be structurally solid (even in abstraction/nonlinear narratives) - you must guide your audience to what you want them to see and know... the audience can wonder but do not let them wander. Stephen King and Michael Chrichton are two examples of writers who understand and execute these essentials consistently.

Anyway, I'd be rambling if I go on anymore and as we've seen from this film rambling isn't a great way to get your point across. So I'll stop here, like the film should have considered doing somewhere near the middle... just gut out all the excess cutaways and literally cut to the heart of the story.

The End.