In the future, try drip acclimating. Let them drip acclimate for several hours or even overnight. Also, never put the water from the bag into your tank. It probably contains copper and copper is poisonous to just about everything except fish.
Only add one fish at a time and then give your tank a few weeks to adapt. Do this for a couple of reasons. First, as you add fish, you increase the bioload on your system. The bacteria which are responsible for your tank's filtration need time to grow to adapt to the increased bioload. This usually takes about a month for them to grow and multiply to satisfy your new bioload.
Second, fish need time to adjust to their new surroundings. They scare easily and like to know where they can go to hide. When you add several at a time, you have a bunch of stressed fish with no fish being dominant. They are all scared of the tank and of each other. They will take longer to find their roll in the tank society than if you just added one at a time. As a tank matures, each fish settles in to it's place in the tank socially. There is a sort of pecking order. When you add a new fish, he quickly learns where he fits in to the order of things and "knows" what to expect from the other inhabitants. When you add too many, the learning curve is longer because none of the other fish know where they belong either. Stressed fish will die or quickly succumb to disease.
At this point I would reduce feedings. This will slow their metabolism down some and help them resist disease better. Also, distract them as little as possible. That's why I recommend covering the tank. They have a hard enough time adjusting to your tank, they also don't need you outside gawking at them, scaring them further.
