Are you going to use tomatillos?
One of the best ways to make it is to buy fresh amarillo and new mexican green chilis (there are a couple names they go by, but the fatter dark green ones and the longer lighter green ones) and roast them. I use my broiler. Coat them in oil and put them close to the flame. Keep an eye on them and turn them once the skin has started to blacken. You'll probably have to do them in several batches. When you pull them out put them in a brown paper bag and roll the end closed. They sort of steam in the bag while they're cooling. Once they are all done and cool enough to handle remove the outer skins. Then chop them up into pieces your blender can handle. Then blend them, along with jalapenos or serranos to taste (for a large family gathering probably just leave out the hotter peppers).
Meanwhile, chop a pork loin into cubes. I like smaller cubes, about 1/2 each. Oil a heavy pan and heat on high. In small enough batches so that each cube has space around it, brown (dark brown) the pork. Remove and place in large bowl. Now chop a large onion or two. Add to hot pan used to brown pork and cook until soft. Now add the green pepper puree, cup or so of water, one beef and one chicken bouillon cube. If you're using tomatillos throw them into the blender and make a puree out of them, add that to the pot. Add about 1/4c of cumin.
You can chop up golden potatoes and add them if you'd like. It can help to increase the volume if you're feeding a lot of people. But it does decrease the overall flavor so you might want to bump up the cumin and add a hot pepper where you wouldn't have otherwise.
Bring it to a boil. Add pork, get it back to a boil. Reduce heat to simmer and cook for a couple hours, adding water as needed to keep the desired consistency.
You can use garlic if you like. You can also add a can of drained diced tomatoes. It's all good.
Serve with cilantro, refried beans, spanish rice, lettuce, diced tomatoes, cheese, hot sauce, jalapenos and tortillas. Always better to fry the tortillas fresh, but not practical for a large group.