When Sister Rosemary Connelly asked the families of Misericordia residents to help raise $14 million, attorney Burton A. Brown had one word on his mind. Bluegrass. “I also play bluegrass,” Brown said. “I play banjo in my own little group.” Though Brown’s five-person band performs at assisted living homes, nursing homes and for the kids at Misericordia, he had another band in mind to anchor a charity concert on Saturday: The Special Consensus, a Grammy-nominated group led by Brown …