IME123- Welcome to the board. Nice to have you here. I'm so sorry that your friend that you mention was treated so unjustly from the elders and the WT mindset in the elders. I have personally known people who were JW's who committed suicide after having been treated unjustly from elders. Elders are NOT trained to deal with mental illness. But they act as an authority under the guidance of the WT Society. It's extremely dangerous and the WT Society has a lot of bloodguilt on it's hands due to allowing these injustices to happen.
As regards HOW you can gather a lot of unjustly treated people together who have suffered abuse from the WT Society due to mental illness to go for a class action lawsuit against the WT Society- your guess is as good as mine. I would suggest talking to an attorney for a consultation to see what options are available. You'll need all the support you can in taking on the WT Society. Victims of WT child abuse are finding that out for sure. You'll need documentation, good attorneys who know the law. WT Society doesn't like to admit fault for any injustices they commit. I applaud you for taking the time and effort to fight on behalf of these victims. You have my support. I wish you the best and good luck indeed in pursuing it