@commonplace
You normally can't have more than one legendary card with the same name on the battlefield, but let's ignore that for now and say you somehow had four on the table. When your upkeep comes along each Nath's first ability would trigger, and assuming your opponent had four+ cards in hand, they would end up discarding four cards. Each of your four Naths would then see each of the discards, ending up giving you SIXTEEN Elf tokens total. I've skipped some steps and order having to do with the stack that you should definitely be aware of, but that's how it would generally go down.