Need advice on tax return?

Alright well for the past two years I have been helping my mom out by giving her money to help support my little brother who lives with her because she has no job and lives off of a small unemployment check. So last year she acknowledged that I should claim him on my taxes since I provided him with the majority of support through the year. Well this year was the same story, she was planning on allowing me to claim him once again since I provided the majority of his support, but this past week that changed up. She met some random person and is planning on letting them claim my brother so that they can give her most of the tax return back in exchange for a few hundred dollars out of it. However I have my brothers social security card since my mom is so irresponsible she would probably lose it, and I'm considering claiming my brother again this year since I helped him out so much. My mom is claiming that she will report me if I claim him again even though I did last year without a complaint from her. Can I still claim my brother even though he did NLT live with mw but I provided the majority his support. Who's at a better standing at this point? Me or my mother who hasn't worked for two years, let me claim him last year, and is only going to let someone else claim him so she can receive the majority of the benefits.