Tactics? Hezrou could do blasphemy, blasphemy, etc every round. That would be cheesy though.
Bebiliths can cast web to try to limit the mobility of PC's, at best they'll make it out of the web in peicemeal, and the ones in the center of the web should be the spellcasters. That means the party is sort of divided up with full cover between them probably, ample opportunities to divide an conquer.
Hezrous can cast deeper darkness, and they have +22 listen with the blindfight feat. 25% chance of missing and taking half damage compared to the PC's with a full 50% chance of missing and only doing half damage is nasty. Plus some might fail and be retching the whole time, their buddies will not know where they are.
Combine the two and you have quite the battle. The wizard and cleric (who were in back) struggle to emerge from the web only to find that their fighter has been facing the Bebilith and Hezrou single-handedly for a few rounds. They don't see this though because of the darkness. Did they prepare true-seeing? If they did then the Hezrou can use dispel good to automatically dispel it.
If you start losing teleport away to maybe get healing from a friendly cleric and teleport back into the fray to keep going. Having a retreiver along helps loads for finding your way back into combat. Planar Binding 8 Formian Wokers will give you a cure serious wounds every round. Best done away from battle, but I suppose they could be binded to be the "healer" of the demons for quite a while. Seal them off in a well-guarded area and teleport there when wounded. 2 minutes later come back again for more! You won't run out of spells nearly as quickly as the PC's will. Buy some granite statues from humans, use them as payment for when you do services for them. Keep them in a store room and when in an emergency use your animate object (at will) on them to create some quick disposable creatures to aid you. You can teleport at will with 50lbs of objects. Bring along a small statue of about 13 cubit feet or 50lbs, when almost in battle animate it for some help. Have it grapple the wizard.
Breaking it up into rounds is hard, no plan survives contact with the enemy. Divinde and conquer, use your strengths.