PvP join as group

[Ualaa]

*Edit*
Read your post wrong.

Not sure why your toons would not join as a group.
Verify it is not an addon.
Disable all your addons, and try to enter as a group.
Be sure you're grouped when you do this.

If it works...
Enable the top half of the addons.
To learn which half of your addons the issue is in.
Then enable/disable half of the portion the issue is in.

If it doesn't work.
Try deleting your Cache folder

Possibly rename your WTF folder after that.
Which is all your saved variables.
You'll ideally want to restore most of those, so don't delete it.

You could try the repair utility.
Not sure if that would find anything.