Palpatine had to have known about the prophecy of the Chosen One and how he/she would bring balance to the Force. Him and Darth Plageius had to stop it. So they had to conceive Anakin (that's another theory for another time, who is Anakin's father). Using the Force or other means, then after Palaptine gains his trust, sees Padme and his mother as obstacles to his apprentice. Yes, I do think he was involved in Shmi's death also. Basically, Palpatine attempted to thwart the Chosen One prophecy and it backfired on him. Palpatine I think planted those visions of death in Anakin's mind, preying on those fears. Palpatine took Padme's life force to keep Anakin alive and told him he killed Padme as a form of manipulation.