Sounds like you might need a lawyer.
I'm not one and cannot suggest what to do in this case but I can tell you my experience.
I needed some
elder law advice recently and looked on the Ombusman website for my state (Georgia) and it referenced a legal helpline that I was able to call and get some extremely helpful advice at no charge.
I don't know what state you're in, but here is a web link to the Ombudsman program in Georgia. http://www.georgiaombudsman.org/
The way I found the legal helpline was by clicking on the "where we are" link, finding my area, and looking at the email addresses for the contacts. I then found the website for that organization and found the number for the helpline.
When siblings start this kind of thing it can be not only hurtful but stressful as well. Your brother should not attempt to use your mom as a bank. He needs to realize that your mom's money is for her care and to be used at her or whomever she appoints for the task's discretion.
Good for your mom to disinherit him. In my opinion, what HE is doing is an attempt at elder abuse.
Be sure when you have your meeting to report the yelling; you might even take your mom with you and suggest that the investigator discuss the situation with your mom both with and without you.