A controller doesn't just seem to about AoE damage but also about affecting battlefield conditions on a large scale, so they're more useful than just for minion-clearing.
As for a second role? Keep on the Shadowfell doubled up the defender role, and that's probably a fairly good choice. They're solid and reliable on both offense and defense, and two defenders plus a striker probably provides a great deal of opportunity for synergy between the three, more so than if two strikers are in orbit around one defender. This is probably particularly true if you're dealing with newer players who may have more trouble keeping multiple delicate members (two controllers especially) out of harm's way.
My gut instinct says two defenders. To determine *optimal* party performance, though, we'd need to have a better look at the classes and their powers.
At will attacks: For the controllers, this is the equivalent to the Wizard's crossbow. It isn't supposed to do all that much. Almost all at-will attacks in the entire game will be damage dealers.