“Passed away” is used when talking to someone who knew the person that died, and within close time of the death. “Passed on” is similar to “Passed away” But implies the existence of an afterlife, therefore would be used when talking to people who believe in an afterlife. You can use passed on (to somebody) give something to someone else, especially after receiving it or using it yourself ,Pass the book on to me when you've finished with it. I passed your message on to my mother. Much of the discount is pocketed by retailers instead of being passed on to customers.

Passed away is the way to say that.

Passed away is more common.

They are the same in American English, but we usually say "passed away". Saying "passed on" sounds more formal to me.

Both are used equally, in the USA anyway. May be a cultural component to how people word those topics. But they certainly mean the same thing.