Given the tendancy of Indian rail lines to be overloaded (and for beggars and hobos to hang on the outside of trains or on the roof/undercarriage), is it possible both are true? That he was seperated from his brother, but both somehow got on the same train and his brother 'fell off' somewhere along the way?

Pure speculation, but it might put your OCD at ease.

I think this is right. Also, it's quite sad to consider the older brother's fate. After he lost his little brother, he may have spent the remainder of his life searching around the train station for him.