I'm really glad that you are getting family support and not hiding this from your daughters, as this will affect them too later on...
As long as you keep moving forward, addressing this, you will eventually find the best method to get him help.
I do worry that he might get angry and do more than rip the door off the bedroom. One extreme measure would be to remove the door from his room if you feel he is doing drugs...but that is usually reserved for young kids.