Are Quests different on normal vs hard vs vhard?

[Neinth]

So I have gone through vhard and skipped the quests because I wanted to do them with an online friend that I'm waiting for him to get the game. So I'm wondering two things. 1st: Is anything different if I do the quests on normal or hard or vhard. Are hard quests only avail if I beat all the normal quests? Is there even a difference? 2nd: Do I have to do quests offline before we can do them together online?
How does that work?

[Jim2001]

The only differance, at least between normal and hard, seems to be that the monsters are stronger and so are the NPCs so that it isn't too much more of a challenge. The offline quests are completely different from the online ones, so you don't need to save them. Also, if you beat all the quest on any difficulty than they all open up to play as much as you want.