Question: Who laced the cookies that were given to the children with arsenic? It's never shown who applies it, only who takes the cookies to them.
Question: It's been established that the grandfather has no knowledge of Corrine's children. When they come across a copy of his will, it states that if it was ever discovered that Corrine had children from her first marriage, she would lose everything. Since he never knew he had grandchildren why was this clause ever added?
Answer: Because Connie and her husband were related (he was her uncle) and any children would be a product of incest. And if it was ever found out they had children, it would bring shame and disgrace to the family name.
Answer: When the children discover the cookies had been poisoned (revealed by the death of their pet mouse which ate part of one of the cookies), they suspect their grandmother. After all, she was the one who had been cruel to them all along. But eventually, they realise that it was in fact, their mother, Corinne, who was lacing the cookies with poison. She was doing so with the hope that the children would eventually die, seemingly from disease. In doing so, she would secure the family inheritance which was contingent upon her never having had children from her first marriage. They eventually confront their mother on the day of her second wedding, and a struggle ensues which ultimately leads to Corinne falling to her death from a balcony.
Michael Albert