Can you play with your friends?Follow

Im pretty sure you can level with anyone one you want..

As it stands right now, the farther removed in level you are from other members of your party, the less experience you will get from creatures. It takes a noticeable gap to create a noticeable effect. And while in the grand scheme of things, experience from creatures will make up at least half your exp, quests are not insignificant and work a little differently. (When people say quests are better exp than grinding, they are taking into consideration the mob kills that occur during the quest.)

When you do a quest, you must do three things:
1) Go to the NPC giving the quest and accept it, which adds it to your quest log.
2) Do the quest. This will usually consist of killing things, collecting items off corpses, or traveling to and talking to someone else.
3) Report to the NPC that ends the quest. Except in the travel-type quests, this is almost always the person who gave you the quest. You will receive experience, monetary rewards, and possibly unlock another quest.

Phases 1 and 3 are done strictly by the individual. I can get into a group to kill 15 Crushridge Warmongers, and supposing that everyone has the quest, they can as a group kill just 15 to each complete the quest. However, every person has to have the quest in their quest log, which they must do themselves. (Someone who helps with the quest and gets it later must start from scratch.)
Likewise, the act of getting credit for completing quests is your own venture. If a quest is worth 3000 exp, you and only you receive that 3000 when you click "complete quest" at the end.

In English, what does this mean? Grouping to randomly slay things will tend not to be very profitable for a party of mixed levels, however if they have the same quests, they can all do them to some benefit. Even if they don't, they can help each other anyway, and since some quests aren't feasible to be soloed, this is sometimes even necessary.

A friend of mine started a new character and asked me to help her get experience. So I took her to a zone I knew well and we ran through all the quests in due fashion. In 3 hours, she had basically run through all the quests in Darkshore (level 10-18 area) thanks to my help. She only gained maybe 3 levels since she got negligible exp from anything besides quests, but I was able to help her.

This is an extreme example. Your friends should be, if anything, asking you for assistance with specific quests, rather than giving them the tour of the zone. But yes, while you can't group with them for exp grinding, you can help them get experience and rewards from doing quests.