Does one have to be an lawyer/attorney to have the power of attorney? My brother has applied power of attorney for my mother who has senile dementia.

Ok, no power of attorney has nothing to do with being an attorney, power of attorney merely means they can sign for the other person if they are not available or unable to sign.

BUT, if your mother has dementia, he does not need power of attorney, since that does not allow him to make her choices, only sign for her, he needs ( or someone needs) guardianship. Why did not both of you not try to be joint, perhaps requiring both of you to sign before any money can be spent?