About the brother
I'm thinking that he could be a older brother that is some kind jealous of his little sister having a boyfriend and he do not have anyone, that could be a start to make a conflict with him and the couple. I'm thinking about at some point of the story, the brother could be pissed at something(maybe a blackout, so he will not be able to be at the computer). And then he would start to be really weird, and at some point watch his sister and her boyfriend sleeping... Something to make the growing of tension and to show how bored and crazy these normal people we see everyday can be actually pretty sick in a three week holiday without their parents. Of course the brother will not be the only one who's strange. But the other characters for other day.











