Yes, you may change to another attorney at any time. It is best to make changes early on, however. This is because much of what an attorney does with a case can't be changed. Also an attorney may be less likely to accept a case that is older.
You will need to consult with a criminal attorney. Posting here will be used against you. This is a public site. Whether his death threats will serve as evidence of self defense depends on a lot more facts that aren't here. Save up for an attorney or apply for a public defender when the time comes.
It sounds as if there is valuable information about the vehicle and owner. We hire our own investigators in cases like yours. At the same time we pursue UM in case the other doesn't work. These types of cases require a very experienced personal injury attorney. You need to select one as soon as possible. Also be aware that there is a two year statute of limitation. You need to file a complaint before two years from the date of accident.
My experts are very important in cases such as this. All evidence must be gathered, analyzed and perhaps get further tests in order to know the answer to your question. Your experienced attorney will know how to handle this.
The court would probably not have dismissed your mom's case. The police involved in the case are often on call, and called in if a plea bargain is not reached. If the police is not available they reschedule. As for the civil suit, she should send the documents to her insurance company and be available to answer interrogatories and give testimony if the need arises.