This has been pointed out already but, the hobgoblins should use range and cover. That tactic is cheap and effective.
Assuming each has a crossbow, they should all pick the same target and pepper him at the longest effective range they can employ. If using crossbows, attack from the edge of the first range bracket or into the second. The advantage of the second bracket is that it forces penalties on missile fire and characters with cleric-type BAB or worse can't afford too many penalties before they start missing a lot.
Targeting priority is as follows assuming the hobgoblins can start the fight at decent missile range.
1. Until a better target reveals himself, all hobgoblins should shoot at the same target to try to put him down or at least mess him up enough to force him out of the fight.
2. If the wizard reveals himself, shift targets to him IMMEDIATELY. He is the only one who may have a serious area of effect attack so he must go down ASAP. Arcane spell casters usually have poor HP too so putting them down tends to be startlingly easy at lower levels. In a ranged fight, the arcane caster will probably be forced to reveal himself to do any damage.
3. Gang up on the barbarian next. He is a much tougher target but he must go down before he gets to chew your troops up. The fact that he has to cover the distance means you may be able to put the wizard down before the barbarian arrives. If you chose your firing position well, the barbarian may have to cross terrain that imparts movement penalties, thus he won't be able to charge you. You will probably need to use melee weapons on the barbarian once he gets close because missile weapons inflict such poor damage unless the user is specialized in their use (and I doubt the hobgoblins are).
4. The cleric goes next. A low level cleric is not an offensive magical threat, but he is a more valuable target than the bard. He can potentially bring downed PCs back into the fight. Being a dwarf his mobility is poor, so as long as you aren't very close, there is little he can do to you. If the barbarian charged and went down, the cleric probably won't be able to reach him quickly.
5. The bard goes last because he lacks the ability to really inconvenience you, especially at longer ranges. He may be able to heal someone a bit, but he isn't a threat to you offensively, and he isn't much of an asset to the PCs defensively. Therefore he is the lowest priority target.
Tzarevitch