I've been wondering if they were actually ALL very close.
To me it seems that they are more like two pairs. Maddie and Kaylee are from Idaho, grew up together, considered themselves to be sisters, and were seniors.
Ethan and Xana were respectively from Washington and from Arizona, he was a freshman and she was a junior, and they were a couple.
The two pairs spent their last evening in different locations and horribly were all slaughtered after having at some point reunited at home.
Then there was another pair, if it's accurate that two roommates were home and unaware of the massacre in their own residence.
It definitely makes me wonder, like many others here, if just one person was the target and the others were collateral casualties. Perhaps someone woke up and tried to call for help or tried to intervene, but I still feel that there was either one target, or one pair was targeted.
However this happened, it is terrifying.