Hi, your brother might be autistic or have borderline IQ or any similar disorder. This can only be ascertained by formal testing and interviewing him.
If he is this way since birth, may I ask what is bothering him and or you now? How is his non expression of his emotions bothering you or him.
Next Steps
Kindly meet a psychiatrist and a psychologist for diagnosis and management.
Health Tips
Remember if this is since birth, not much can be done. But a good try is really worth it. All the best.