Specific questions regarding multiplayer (HC)

Hey guys, my first post to reddit ever and i choose this sub to start with.Everyone has solid and upbeat advice so i thought i'd give this a shot. I've googled my question to death and, while answers dance around it, i've found not found the solution. My question is: Can my brother and i play together over live with very different leveled characters (both HC) and enjoy the game? Background: I am lvl37 DH, he is lvl 21 monk. I joined his game last night (back at act I) and first contact with the easiest bad guy he gets one-hitted and loses everything. He creates another character and wants to join my game instead (i had a bad feeling about that but w/e) and same result. Now, is this because of hardcore? I feel like i'm missing something super easy, or it's just not wise to play together until lvl 70 on both characters. For me, hardcore is suuper fun and i can't see myself not playing that way but it looks like i miss out on a lot of the benefits of the game itself, like playing with my brother. Any help you guys could give would be appreciated, sorry if this is nothing new asked but i couldn't find it anywhere.