Where can I find help for my disabled brothers, who is being taken advantage of by his immigrant (U.S.Resident now) wife?

My brother, a physically and mentally disabled person (who doesn't think he's so mentally disabled) married an illegal immigrant 3 1/2 years ago. No one in our family felt good about this but of course he thought it was genuine. The fit just didn't make sense. Though we love our brother, and he is kind, we couldn't see what she would want in him as they seem the odd pair. They could barely communicate,his ability to reason falls below the average person and she would have to provide MUCH care. She on the other hand, she was a very intelligent,strong, levelheaded person. My brother had his income from two sources and though we hoped it wasn't for the $, he was a job for her, she was a hard worker and was willing to take the tradeoff. Our family has tried give the benefit of the doubt but she causes us to question so much. Now she is building a VERY nice home in Mexico and while there, said my brother adopted her 35 year old son, who now has our last name.