Abilities would seem to be fairly average, so I'm guessing somewhere between the chain devil and bone devil. How about Str 18, Dex 15, Con 15, Int 10, Wis 12, Cha 13? Or somewhere around that?
Maybe boost Dex to 16, since they've got heat-vision. Ranged feats might be appropriate here--Point Blank and Precise Shot, especially if they work in packs.
How do we want to handle the eye rays? Should it be able to fire one as an attack action, all three as an attack action, or something else? A retriever can fire one per round as a free action, while a beholder can fire all of its eye rays as a free action. Should we allow them to be used every round, or have a recharge period (like the retriever)?
Average flight maneuverability. Nothing suggests that they're masters of the air, but they're medium size and pretty dextrous. On the other hand, giving them good maneuverability (or the Hover feat) would let them sit out of reach and pick people off with their heat rays.
I don't want them firing off their eye beams as a free action, that's for sure. Perhaps no recharge time, fire one as a standard action and all three as a full-attack action?