Where can I find the Family?

So, first off, if you don't want to work for it:

You'll find the family in a Metro station under Meresti trainyard, about 3 squares east of Arefu.

Evan doesn't have all the info, so he won't send you after the Family directly. You've got two options. Option number one is to inspect the victims a bit more closely with an extremely high (90+) Medicine skill. This gives you the evidence you need to get Evan to send you in the right direction - ask him about it, and he'll tell you where to go and mark it on your map.

Option number two is to explore the locations listed a bit more thoroughly. Specifically, head back to Northwest Seneca Metro, and be less afraid of radiation and more diligent in your interior explorations.

Oh, and watch out for traps, and it's probably for the best if you don't barge in on The Family guns blazing - they have quite a bit to tell you.

In Seneca Station, where the ghouls are,

there's a back room with radioactive barrels and such in it. There is also a manhole cover that leads to a passage that will take you to the train yard. There are multiple train cars that you'll see when you exit the passage into the yard; on the other side of those train cars is another passage that will lead you to the station with The Family.

You'll want to be careful, though. They don't like unexpected visitors ...