The best advice I can give you right now is to get in to see a criminal defense attorney as soon as you can. There are many questions to ask to decide where you are in the process and what is the correct course of action to take. If there is a warrant outstanding that will be the first thing to tackle; you don't want to get arrested before you have a chance to speak to an attorney.
The defense does have disclosure obligations under the discovery statutes. If the evidence is going to be used at trial, the defense may have to disclose it prior to trial or the prosecution may be able to have it "excluded" from the trial, or some other less onerous remedy. Exclusion is not the same as suppression, as pointed out, but the defense is not entitled to avoid statutory procedures and sandbag the prosecutor (unless you have a very schrewd attorney and the right situation!)
It means that the DA is alleging that you have a blood alcohol of .15 or greater, or refused to take a chemical test. It probably means that one count applies to each count of DUI, and is usually alleged as an enhancement to each count. It means that the judge can increase penalties on either count if you are convicted and those facts are found true. You need an attorney to help you with this case if only because of these allegtions.
How close are you to completing your courses? If you have done all but a couple that is one thing. If you haven't started, that will be another. Either way, your best choice is to ask the judge before the time runs out because if it does and you haven't finished you run the risk of a violation of probation. If the judge does grant you another extension, finish it this time...no excused!
Yes. Report it to the police. They will conduct an investigation and if they develop enough evidence charges will be filed by the DA. These are not easy cases for anyone, especially the victim, who will have to recount the incident(s), and testify if necessary. There are support groups and victims' advocates services she can use to help her through the ordeal. That it has been two years does not help but it does not preclude going forward.
If by "disposed" you mean dismissed, then no conviction will show on your record and you can answer that you have no convictions (unless you have some other conviction). But if "disposed" means that you entered a plea of some sort, then you have a conviction. You will need to be a bit more clear.
Your brother really needs to get to a qualified criminal defense attorney as soon as possible. As I am sure you know, this is a very serious situation. He should not make any further statements to law enforcement, or post anything on any social media site about the incident. Avvo is a great place to start his search for an attorney; by reviewing profiles and reading about the attorneys, he can chose one or more with whom he would like to consult. Many offer free initial consultations, but that...