The guilty pleas come one week after co-defendant Paul Cassidy pleaded guilty to similar charges and three months after fellow gang member Michael Crawford - the person whose items were stolen - admitted to having orchestrated the shootings.
Crawford was sentenced last month to seven years and four months in prison. Nelson-Bell and Cassidy both await sentencing in October.
Others have pleaded not guilty and await trial.
Police said more than two dozen people were believed to have been involved in the shootings, arriving from as far away as Picton after organising a meet-up via a Facebook Messenger group.
It appeared that high-powered semi-automatic firearms were used in the shootings, Justice Grant Powell said at Crawford's sentencing, describing the group as having felt "they were entitled to storm through communities in Ōtara, shooting wildly and recklessly as if they owned the place". He referred to the 2020 shootings as a precursor to the "reign of terror" in Auckland earlier this year due to rivalries between the two gangs.