Diablo IV - A Return To Darkness

Couple of questions for the group.

Does anyone know the in-game mechanic for when multi-player events are involved. I’m not talking about people forming groups, I’m talking about when you see something going down on the map and there are others there or others join you and you’re level 40 and here’s a level 30 and there’s a level 20… am I making this up? How do they calculate the combat if we’re all hitting the same mobs?

With regard to aspects on your legendary gear, does anyone know how it plays if you happen to have two of the same type? Say… something creates a barrier (?) for you that lasts 10 seconds and 30 second cool down before it happens again. If I have two of that type aspect do I trigger a second barrier before the 30 seconds for the first expires?