Five large institutional investors are planning to file suit against the Royal Bank of Scotland Group plc (NYSE:RBS) (LON:RBS) next week, claiming more than £1 billion over the bank’s 2008 rights issuance. Legal & General, Standard Life, Prudential, Aviva, and Universities Superannuation Scheme have appointed law firm Quinn Emmanuel to represent them in the case, reports Steve Slater and Chris Vellacott for Reuters, taking the total claims against RBS over the rights issue to more than £4 billion. Acquisition of ABN Amro made RBS vulnerable when the crisis hit Royal Bank of Scotland Group plc (NYSE:RBS) (LON:RBS) acquired the troubled…