With assets of $11 million from a lead-poisoning case against a Chicago landlord, it makes sense for Donald Howell to get an estate plan. But Howell was born with profound cognitive impairment.Relying on the “substituted judgment” doctrine, his co-guardians, Northern Trust Co. and LaTanya Turks, argued Howell would want his money to go to Turks, his mother and full-time caretaker, rather than also being shared under Illinois intestacy law with family members — his father and 10 half-siblings born to 10 …