It sounds like the howling that you are discribing would be the coyote serenade, when a group of coyotes does this it is thier way of telling the other coyotes where they are and that this is thier territory. Often times, when one group do this, other groups will soon follow, and that is why the "coyote serenade" on the fox pro is so effective as a locator call in the evenings.
Lots and lots of calls on the market will work just fine, all of them will work sometimes. As long as you have a good idea of what the sounds should sound like. I'd suggest buying a calling video, or two, lots and lots of them to choose from, and watch and listen to how calling is done. It's not hard, but you'll do better with at least some knowledge to how to do it to start with!
If you go to the Predator Masters web site, you'll find lots and lots of info. about calling predators.