Thanks for the input, guys. I realize I made some rule/tactical errors (im not going to deny that), but hopefully will be able to better run the next game.
Some points...
The Cleric had slay living prepared because the cleric wasn't expecting anyone to come and try to attack the temple - - he didn't know he was going to be taking prisoners. He had cast it because he had just taken a good deal of damage due to the rogue. Figuring 4 prisoners work as well as 5...
While the spell could have done its job next round, he was already held by then.
The four additional clerics were thrown in because at 3am, the battle with the other four was just going on and on. The other four were in the temple but not stationed at that area. I couldv'e left just the four and continued with the clerics taking a few more rounds to try and subdue the party with melee attack, but based on the rolls so far - that couldve taken ages. Maybe that was another error on my part.
Perhaps I should take another read over the PHB, or find someone else to DM next time.