The deranged 15-year-old accused of slaughtering all but one of his family members in their ritzy lakeside Washington mansion was kept isolated from the world and raised under a “rigid, militant survivalist ideology,” his lawyer claims. Mark and Sarah Humiston drove their future killer son to the heinous crime after hammering him and his siblings with years of religious extremism and government paranoia, according to court documents filed last week. Prosecutors say their oldest son — whose identity has been kept under wraps — shot his parents, brothers Benjamin, 13, Joshua, 9, and sister Katheryn, 7, in the middle of...