Based on the recipe you shared with me, it looks like we are on the right track.
The green chile that recipe speaks of is the New Mexico variant of an Anaheim. If you don't have access to them, use Anaheims.
The other green peppers are indeed a mix, though probably mostly the mild green bell pepper. Their purpose in the recipe is to provide bulk, color, and mild flavor. But they mention mixed as this is where you'll control the heat of your chile verde. Besides the green bell pepper, you could include green jalapenos, more New Mexico/anaheims, poblano (these have a tough skin and should be roasted and peeled) and so on.
Peppers are a natural product and as such, their flavor and heat can vary quite a bit from pepper to pepper even of the same variety. The instructions mention to taste the chile verde and use these mixed peppers/chiles to build the level of heat you're looking for. If the chile verde is hot enough with just the New Mexico chiles, use just green bells or other very mild peppers/chiles.
Let us know if you have other questions.