You've asked a lot here, but here goes. The rule about not being allowed to have an attorney represent you in small claims means that the attorney can not speak for you in court. He or she can come with you and sit at your side and advise you up until you get up in front of the judge. What he cannot do is speak for you to the judge.
As to the other side choosing the commissioner, its not clear to me what the purpose is in your case, other than perhaps causing a delay. In wrongful detainer cases, I was once advised NOT to agree to a commissioner, but instead to demand a judge. I'm not sure if there is somehow a benefit to a defendant having a commissioner in a case like yours. Hopefully, its not a question of defendant's attorney knowing the commissioner well or NOT liking the judge that would have heard your case.
You should be allowed to use the film footage in small claims court. I suggest you check with the court in advance and see if they are set up to assist you in showing it. If not, you should be able to simply present it on your laptop, but check with the court about this too . . . in advance. In small claims court, the only individuals that need to see what you present are the judge, the opposing party, and you. So my guess is the judge will allow you to bring your laptop up to the front of the courtroom where the three of you can view it together.
Best of luck.
Simple answer is YES, the footage is evidence and would in all probability be admitted.
You will need to write and confirm that they do not destroy, lose, or overwrite the footage, and have a subpoena issued to have them bring the footage to court. Bring your laptop and BE READY to PLAY. Tell the court what you have and that it is unedited. Have the friend there and have the friend preview the tape so the friend can narrate what she saw: standing and watching, backing out, while in process of backing out ... it was THEN that the other backup lights came on, saw your mother stop, saw the other back out and STOP, and saw the other ... suddenly...... lurch/crash ...... that is what I READ from your note.
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