Ill put the bag in the tank and leave it their for 15 min then I put water from my tank in the bag and let it sit for 30 min. then i put them in.
This might be the problem. I drip acclimate all of my inverts for 2+ hours. When you put the bag in the tank, that is to get the temp in the bag the same as the tank. When you add a good amount of tank water in the bag, that doesn't give the critters a slow acclimation period, this might be causing then undue stress and shock. I like the drip, because I set it up and let it drip, no measuring, just watch a movie (and the cats and dog, they like to sniff) or do something, come back and add them to their new home.