I'd go Iksar and make the group Shaman, Necro, Monk. Lizards are always "cool" to kids, there's lots of leveling zones close to each other, and Kurn's tower is pretty badass for them to enjoy.
Both have feign death at later levels, older one plays the monk so he can do the pulling (forget about split pulls, just have them man up), younger one plays the necro so he can just sent in pet and lifetap or whatever else. No need to any advanced tactics.
As for the experience penalty, who cares? This game is about leveling and enjoying the ride so delaying it a bit won't hurt anyone.
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