A news release says the families will speak Tuesday about some behind-the-scenes events that they believe need to be discussed. Group spokeswoman Anita Busch declined to elaborate.
Twelve people were killed and 58 injured or wounded when a gunman opened fire on July 20 during a midnight showing of the latest Batman movie in the Denver suburb of Aurora.
Charges against James Eagan Holmes include murder and attempted murder. He's being held without bail and hasn't entered a plea.
His defense lawyers have said he is mentally ill.