If someone has a save file like that, it would definitely be hacked and not all Pokémon would be legal, since Zacian, Zamazenta and Eternatus are shiny locked right now (other shiny locked Pokémon can be bred). You say that your Switch is already banned. This means that you most certainly have a hacked Switch, which in turn means you can use PKHeX in order to cheat your shinies on your own and import them into your save. I don't know and don't care about Nintendos politics on having hacked Pokémon on an unbanned Switch, but if they wanted to, your sons Switch could become as banned as yours as soon as they find some impossible Pokémon on it (even though I doubt they'd go that far).
