It can take some time for them to figure out who's the alpha. I suggest that you only let them play together when you are home and even then they should be on leads. I would leave the leashes dragging while they socialize so that you can pull them apart if there is an emergency.
You might also want to try a homeopathic anxiety reliever for some or all of them. Homeopet (www.homeopet.com) works great and can be a lifesaver.
I also suggest that you choose an alpha. Feed this one first, play with this one first and let this one have first dibs at sitting at on your feet. Once you choose, you have to stick with it.
Let me know if you still have questions.