Mothers and Sons **1/2
                        By: David ShewardFrederick Weller, Tyne DalyThe most affecting moments in Terrence McNally's Mothers and Sons are silent. These take place when Tyne Daly as Katharine, a Dallas widow, is left alone in the gorgeous Upper West Side apartment of Cal, the lover of her late son Andre who died of AIDS 20 years earlier. Informin…