Bride’s Maids date back to when the Bride would have ‘bride’s maids’ who would wear exactly the same clothes as the Bride – evil spirits would get confused ensuring only good luck prevailed for the Bride!
In later times the Groom’s friends dressed the same as him, the Bride’s friends the same as her – this confused any potentially jealous suitors who might kidnap the Bride, or worse – kill the Groom!