I'm angry at my uncle
Why are you angry at your uncle?
He drinks all our liquor and says it's somehow owed to him.
That must be really annoying. Sounds like you'll have to explicitly impose some boundaries on his presumptuous behavior.
It's not an option. He has dementia and thinks that he worked very hard to earn all that.
Oh so it's not his fault either. You should treat him compassionately and show care for him in any way possible. It's better to hide your liquor from him.