Interestingly, Supapapa, Google gives the translation as "¿Cuál es su hermano llamado", which is midqway between the two previous answers. (It translates as "What is your brother calling himself?").
If their are any native Spanish speakers around here, I'd be interested to know when they'd use 'como' and when they'd use 'cuál'. My suggestion, above could be read as "Why does your brother call yourself" but my school Spanish lessons, together with a former friendship with a Spaniard, has taught me that 'como' can mean 'what', as well as 'why'.