While it is nearly impossible to read the mind of the unknown deputy D.A. who will be reviewing this matter once the police reports are received, the chances that some charges will not be filed are very very low, near zero. Sorry, but with drug involvement and especially the prior background, it is almost certain that charges will be filed.
Although I am an experienced CA criminal defense and appeals attorney, I can not 'guarantee' that my answer is entirely accurate, since I have not reviewed all of the factual circumstances of the case, nor have I discussed those circumstances fully with the questioner. The fact that I have answered this question does not establish an attorney client relationship between the questioner and my self or my office.
Why in the world would you call the DA on a case that hasnt been filed? Do you want your brother to be sent to prison? The more you bother the DA the more likely charges will be brought. It your brother is charged with a felony he will face life in prison.
The above information does not establish an attorney client relationship nor is it meant to provide legal advice.