Party composition and picking classes as a group

[Lopor]

Greetings,

I'm looking to enlist for the forces of Order with 3 of my friends and I'm a bit unsure about class choices. I want to make sure we can participate in all content, both PvP and PvE together. Thus far we have an Ironbreaker, a War Priest and a Ranger. And that's where I come in. Would that be possible if I picked a Knight or should I make a DPS? I thought the Knight could do that if I picked a two-handed weapon, but after some research I am no longer sure of that. Should I just pick a regular 'ol DPS class like the Slayer?

Thank you.