Just out of curiousity, are each of your snakes in their own tub/tank? You didn't really specify. If any of them are housed together that will stress them out. They can also get stressed easily if they don't have identical hides (the proper size) on both sides of the enclosure. Generally speaking if your snake(s) are refusing to eat it is usually directly tied into your husbandry (temps, humidity enclosure setup). If your snakes have had enough space and time to get settled in I would try live prey. As long as you keep an eye on things your snakes shouldn't be at risk of getting hurt. As far as which pet store to get the "food" from...that's totaly up to you. Take a good look and see if the mice/rats seem clean and well fed. If they seem to be well taken care of you should be fine.