It's better ot to argue. There's a reason for his forgetfulness and behavior, which you describe as "childish". I don't know his health history, but it could be Alzheimers - a doctor would have to run tests, etc. to diagnose.
Your grandfather may be aware of his forgetting things and doesn't understand what is happening. This would be scary to anyone. If your aunts are arguing with your grandfather, it won't do a bit of good. Most people are in denial or a panic when they see that things are not going well with a family member. They have to figure out what to do for themselves and stop arguing. They may have to make bigger, more difficult decisions soon, and they need to be on the same page.
