I am so so sorry. I can totally understand not wanting to see your mother going to get him, but until she sees that she is enabling him it is not going to change.
He has to want recovery for himself, and normaly that takes consequences to want it. Serious ones like your family not enabling him anymore.
My heart really goes out to you. Is it possible your mother would go to an addiction counselor with you? It would likely help you both. Also NarAnon or Alanon and/or Celebrate Recovery would give you a face to face support system.
When you do let him know you know about the stealing, do so with calm detatchment. It's a fact I know you did X so you can no longer be in my home and I am no longer willing to help you, etc. That is sitting a boundary for yourself and telling him the boundary. I caution you, say what you mean, and mean what you say. Addicts are like naughty children and will play you like a fiddle. No need to be angry, just matter of fact and very calm. Only say it once. Write it in a letter if you have to.
You don't at all sound scattered. You sound distressed which is totally normal given the circumstances. I am so sorry you are going through this and sorry for the reason you are here, but glad you found us.
Keep posting, you are not alone.