Why does your party's AC vary so strongly?
Anyway, with +12 to hit, the owlbear won't be reliably hitting Mr. or Ms. AC 26 with both attacks. Said character (a defender, I suspect?) should tie up at least one owlbear while getting some healing backup, preferably with anything that can boost their AC even higher. If you have a rogue, all the better -- dish out the sneak attack damage! The owlbear might want to maul the rogue, but they'll be doing so at -2 to hit since the defender will be marking them, and if the defender is a fighter, I think they get a free attack if that happens, whereas if they're a paladin, the owlbear will be taking divine challenge damage, which (as an unintelligent creature) it should avoid even if the tactical considerations mean it should keep trying to eat the rogue.
Furthermore, if you have a wizard (or maybe even a warlock) you can mess with the powerful attacker's mind. Elites no longer get a defense bonus, so target those Will saves. Hitting an elite with, say, a single-target power that restrains or dazes it is like hitting two opponents with a similar power. The rogue's Blinding Barrage (if you have that) virtually guarantees the owlbear won't be hitting anything for a round. (Note that rogues get a very high attack bonus when using throwing daggers...)
What is your party composition anyway?