A group of bondholders plans to challenge Bank of America Corp’s $8.5 billion settlement with holders in soured mortgage-backed securities, saying it may be unfair to other bond investors. In court papers filed Tuesday in New York State Supreme Court in Manhattan, 11 companies sharing the name Walnut Place said they had “serious concerns about the secret, non-adversarial, and conflicted way in which the proposed settlement was negotiated and about the fairness of the terms.”