My family based green card is pending with USCIS due to background check from 3 years. Need an expert laywer in Nassau county NY for Writ of Mandamus

This is regarding my brother's case who filed an immigration based on marriage to a US citizen. The case got filed in June 2014. He is now having 10 months old daughter. First interview happened in January 2015 and second interview in Feb 2015. Nothing is moving at all since then. Lawyer who filed the case wrote letters to get the update and every time we get the same response that it is under background check. My brother went to USCIS info pass appointment in Oct last year. USCS says there is nothing pending from their side. Its the 29 agencies they are waiting for the response. USCIS officer wrote email to them as well during the appointment but nothing is happening. This is quite frustrating. He and his family cannot make decisions for future life due to this hanging situation. We are looking for an expert who has experience with similar situation and has 100% success rate in writ of Mandamus. We can also consider some other solution if you have any.