Lyn
Thank you for your question and welcome to ADHDCentral.com.
It sounds as if you are helping your grandson, just by being there for him and listening. However, you may want to consider asking your grandson if, together, you can talk to his father about the situation at his mother's house. Maybe your grandson will feel more comfortable talking if you are with him and he knows there is someone that will believe him and be on his side during the conversation.
Eileen