Please bear in mind that my understanding of the federal court system is limited - my experience is more with state systems - so if I get something wrong, please correct me.
The defendants in the case have until 11/20 to answer the original complaint filed by the plaintiffs. Basically, they have to submit a paper saying, "No, I didn't do this, or this, or this." They have to rebut every accusation from the original complaint. Most likely they will also submit a motion to dismiss.
In regards to more plaintiffs being added: the original complaint requested class action status. I didn't see anywhere that the judge has certified the case as a class action yet. If he does, then plaintiffs can be added throughout the process - I'm not sure if that would delay the case but it may if the discovery process has to start anew for each plaintiff. I'm not sure if more plaintiffs can be added if the case is not certified as a class action.
Hope this helps.