Thank you for using our forum. My name is***** am another expert on the site, your prior expert opted out, and I hope that I can assist you today.
While you cannot sue on behalf of other tenants in your unit, if I understand your post above, you are primarily concerned with an abusive landlord that is taking advantage of tenants in this HUD (government subsidized) housing unit.
You can report bad landlords directly to the Federal Housing and Urban Development department here: http://portal.hud.gov/hudportal/HUD?src=/complaints_home. HUD can investigate your complaint and take further action (usually administrative action directly against the landlord and/or their management for abusive practices).
Filing a complaint with HUD will protect you from "retaliatory" action by the landlord for a minimum of 6 months under CA law.
You can also sue the landlord yourself for your own claims (so anything the landlord has done to you). CA has a relatively high small claims jurisdictional limit, so you can sue for up to $10,000.00 in small claims court quickly and easily without requiring an attorney. This link to the CA Courts website provides you with information and all of the forms you will require: http://www.courts.ca.gov/selfhelp-smallclaims.htm
(You can provide the same information to your neighbors, they can sue the landlord as well, but they must bring their own claims. Similarly, if they are willing to make reports to the HUD (they can do it online using the link I provided to you above), the more reports that the HUD receives the more diligently the HUD will investigate.)