Your brother must first file an immigrant visa petition on behalf of his wife. A K-3 visa petition can only be filed after the immigrant visa petition is filed with USCIS. There is no fee for filing the K-3 petition but there is typically no benefit derived from filing the petition as processing of the K-3 will cease if the immigrant visa petition is approved prior to or at the same time as the K-3 visa. Given current processing times, USCIS typically approves the immigrant visa at the same time or before the L-3. You can read more about family immigration at http://myattorneyusa.com/family-immigration.
Answered on Jun 02nd, 2016 at 2:53 PM