I believe it is showing how your grandson is feeling attacked by people he loves, specifically his family. Perhaps his sister and his dad are attacking him out of anger or negative feelings. It will process in his subconscious.
I apologize. I will explain to the best of my ability. Depends on your beliefs. So please do not take any offense to my words. Dreams can be very confusing and complicated sometimes as it relates to the subconscious. With your grandson having this dream of his loved ones being attacked is showing how they are being attacked spiritually. This can be result in them having negative feelings or emotions or anger. So if they are being spiritually attacked your grandson will see the result of this in the physical realm.