Only creatures on the battlefield will be exiled. In other zones, they're "creature cards," not "creatures."

If the targeted creature is an illegal target by the time Sever the Bloodline resolves, it will be countered and none of its effects will happen. No creatures will be exiled.

Unless a token is a copy of another creature or was explicitly given a name by the effect that created it, its name is the creature types it was given when it was created. For example, the Beast tokens created by Thragtusk and by Baloth Cage Trap are both named "Beast."

A double-faced creature only has the name of the face that's up. For example, if Village Ironsmith is targeted by Sever the Bloodline, Ironfang wouldn't be exiled.