The bride and bridegroom are in the USAF, so are the brothers of the groom and the brother of the bride. The groom and all the groomsmen are planning to wear their dress blues military uniform. However, the best man who is the twin brother of the groom, is stationed in Korea, and there is a possibility that he may not be able to get leave to attend the wedding. In that case, is it OK to have a stepbrother stand up with the groom in a dark suit since he is a non-military civilian?