I've only watched Day 1 so far, but I have noticed a few interesting things that make me question how real this is.

1) the camera - they make a few comments about how they can't turn on the lights because someone might see from outside through the house's oversized windows, yet they have that camera light pointing all over the place. Plus, the camera doesn't appear all that portable either (in Day 1, pt 4 there's a reflection of the thing), considering these two need to get out at a moments notice. In a dark house, even the smallest light, like the one in the fridge, is going to brighten the whole room.

2) I have two kids, and frequently "detect" their presence throughout the house, especially in areas where they normally aren't supposed to go (my bedroom and office as examples). There are just too many ways to leave evidence in a room (odd scents, footprints in the rugs, moved items, missing food), especially when these people aren't home all day. I just don't see how anyone could go for even a short time without being noticed.

3) the smoking - I lived in an apartment where the neighbor used to smoke outside every so often. Almost from the second she lit up I knew it, as the smell of tobacco is so pungent. If these girls are doing this for real, I'd expect them to give up habits that can so easily give them away.

4) the food - Unless the owners have guests over frequently, I can't see why they would have an excess of food in the house, beyond what they would normally need (my mother had a giant food pantry in the basement, but then there were also six people living there). That being the case, disappearing food is going to get noticed simply because there is less of it to begin with. When I was single, I would buy cereal one box at a time. If it were to suddenly go half-empty, I noticed.

Again, I haven't seen path the first day yet, but already this seems fake.