An Upper Merion man accused of killing a baby girl and her grandmother in King of Prussia last October has pleaded not guilty to all charges.   27-year-old Raghunandan Yandamuri is charged with first degree murder and other offenses.   Authorities say he tried to kidnap 10-month-old Saanvi Venna and killed 61-year-old Satayvathi Venna when she tried to protect her granddaughter.   The little girl was allegedly then suffocated and her body hidden in the basement in the Marquis Apartment building in King of Prussia.   Yandamuri faces the death penalty if convicted.