40% of the American Opportunity Tax Credit (AOTC) is refundable. Your Mom is eligible if she claims your brother as a dependent and he is at least a half time undergrad, at an eligible institution. His age is not a disqualifier for the AOTC*. His age only makes him a qualifying relative rather than a qualifying child dependent.
You have everything else correct. As her dependent, you do qualify her for the Lifetime Learning Credit (LLC). but it is non-refundable.
*Since your brother is over age 23, he is eligible for the refundable portion of the AOTC whether he is claimed by your Mom or he claims himself on his own return. But from what you describe, he is you Mom's dependent and she should claim him.
