Generally...he had passed away, he had died, in UK English. Well, that's in my humble opinion ))

In American English, I’d say that none of your examples are strictly wrong, but they are also probably not the best thing to say for any likely specific situation. In general it would be strange to ‘have an idea’ that someone has died. You would either observe it or learn about it because people dying is important. As far as the use of the tenses, Americans tend to use perfect tenses when the meaning requires it, whereas in British English it can be a stylistic choice. I didn’t know he passed away. I’m shocked. (I’ve just learned that he died and others in my group have been aware of that for some time. ‘Living under a rock’ focuses the situation on me, which is rather callous in a conversation talking of someone’s passing. As an American I wouldn’t say ‘he’d passed away’ because the current situation (‘he is dead now’ ) is conveyed perfectly precisely by the words ‘he passed away’. But there’s nothing wrong with saying it, either. It wouldn’t stand out as being pretentious. It’s just an alternate way of describing the situation.)

The first almost needs a timeline afterwards, like …he passed away 10 years ago. He had is more natural, although even more so abbreviated to he’d.