Okay, peeps. I've think I've completely nailed this one. But we'll see what your opinions are.
First thing's first. We're going to assume that logically they grew up in the United States, but the evidence I can provide for that claim is in 7. pg. 135. The depiction of the house and the dollar sign on the window of the gas station pretty much seal the deal.
So, the real question here is, which state did Emily grow up in, and to do that, all we really need to do is analyze the prelude in 1. We see a bendy mountain road, which near a very large urban sprawl. This rules out any sort of town, because this here is obviously a city. From this, I was able to narrow down the state to either, Washington State, or, California, with Seattle and Los Angeles respectively
but I can tell you with NEAR CERTAINTY, that I know which one it exactly is.
The funny thing about BOTH of these locations, is that Kazu Kibuishi has lived in BOTH OF THEM. (He currently resides in Seattle.) So originally, I thought it had to be Seattle, as Seattle has numerous mountains that border it. That was until I saw this.
I originally knew that he lived in Los Angeles, but doing research on this location. I saw something interesting when viewing the map.
Take a look at the green above the highlighted region. Those are the San Gabriel Mountains, but even more so interesting, was the road that ran through them.
Ladies and gentlemen. I present to you. The Angles Crest Highway.
The pictures match the road in which the Hayes' family drove on EXACTLY. (Did I mention this particular stretch of road has several accidents tied to it's name)
The town of Altadena, which is essentially a satellite town of the much larger Los Angeles, which would be clearly visible from nearby, is but a ten minute drive from the beginning of this road.
How exactly could I be sure that this was correct, and this was the road?
This road also contains many trails, and camping grounds. (Kazu likes biking and mountains, you can go look at his twitter at @boltcity.) It is without a SHADOW OF A DOUBT that he was inspired by this road during his time in Altadena, and included it in his graphic novel.
From this evidence, I can come the near certain conclusion that Emily and Navin grew up SOMEWHERE in the Greater Los Angeles Area, in the state of California (somewhere nice, if not Altadena, (as Navin stated in 1. that they had lived in a large house, and Altadena has large houses lol), and that the car crash took place on the Angeles Crest Highway where David Hayes lost his life.
But hey, refute me if you think I'm making a mistake, and call me out if you think I need to include a piece of evidence I missed or a point I need to elaborate on.
OTHER EVIDENT IMAGES
Picture of a tunnel on the Angeles Crest Highway and an exerpt from 7. https://imgur.com/D0QWaeY
This is a picture of Los Angeles from Mt Wilson at night. (Mt Wilson is the closest Mt to Altadena.) http://medias.photodeck.com/74edc736-9827-11e3-b56d-11cbc5a80957/082612-los-angeles-above-mt-wilson-wide-night-moonset-timelapse-proreshq-HD-2_xlarge.jpg Compared to the first image in the prelude of the 1st volume of amulet, they are near exact.
IRREVELANT CLAIMS/HEADCANON: I truely believe that the Hayes' family resided in Altadena, and that David Hayes worked with NASA At the Jet Propulsion Laboratory close by. I have a way more complex theory about that, and how it ties in with the whole story, but that's for another discussion.