When my father is either around my grandfather (his father) or my oldest brother he literally changes his tone of voice and his personality switches where he just becomes the biggest douche you've ever met. When you can tell he goes into this his tone of voice just switches to a smartass/just plain mean type of sound. I'm a licensed social worker so I study the DSM V but I can't diagnose professionally since it would be against my ethics. Does this fit into a disorder in the DSM V, or has anyone ever experienced this between a family member themselves?

This happens in families. They've probably been playing out these roles for years. I'm guessing it's learned behavior, maybe a defense mechanism, depending on who sets off whom.

You're not ging to change this family dynamic after all these years of it apparently working so well for them. And diagnosing it would be worthless. When my BIL plays this kind of game with certain family members, I get busy with something else or even leave the room, and let them have their "fun."

Do you think anyone is getting hurt during this?

I know I am even though I'm completely used to it by now. My middle brother is getting hurt by it and I know he is because he basically stopped calling him.