Greenpeace volunteer Howell and Ashburton kite maker Mulvay faced one charge each of jumping into the ocean from a protest vessel, forcing the Amazon Warrior to stop its seismic work.
Diversion for the pair and Norman was raised at an earlier court appearance, and on Thursday the single charge laid against Mulvay was dismissed by the judge because he had completed diversion.
Norman and Howell appeared before Judge Nevin Dawson on Thursday morning where a judge-alone trial date was set for April 30, 2018.
Mansfield noted it was expected the trial would take one to two weeks and there would be considerable defence evidence, including expert witnesses.
Speaking outside court Norman said the bigger issue at hand was that the government had passed a law that "criminalised protest" and were now prosecuting climate activists.
The group were charged under the Crown Minerals Act which has new provisions making it an offence to interfere with, or get closer than within 500m of, an offshore ship involved in an oil exploration.
The offence carries a potential penalty for an individual of one year in jail or a fine of up to $50,000. For an organisation, such as Greenpeace, the fine could be up to $100,000.
He said it was critical climate activists were able to stand up for what they believed in.
"The government passed this incredibly restrictive and anti-democratic law and now they're using it to stop people who are climate activists."
"In order to stop oil companies finding new oil and burning it it's essential that people take action in order to protect the greater good and that's why we were out there that day and that's why we are not guilty of the charges."
The defendants would be using a "greater good" defence, he said.
"We're not denying we were in the water out there, what we're saying is we had to do it in order to prevent runaway climate change.
"We'll be bringing experts in from around the world who are climate experts about these issues and we won't back down. As Tom Petty said, we're going to stand our ground. This is incredibly important for the future of us and all of humanity."
Howell said she was "nervous" about the criminal charge she faced but believed the action she took was necessary.
"I'd rather it wasn't by breaking the law but it had to be."
New Zealand Petroleum and Minerals/MBIE national petroleum manager Josh Adams said the non-interference provisions of the Crown Minerals Act did not criminalise protest and was about balancing the right to protest with an operator's right to get on with their work.
"Petroleum operations at sea are complex, often very precise and sometimes carried out at an industrial scale by large vessels with limited manoeuvrability.
"Disrupting this work puts lives at risk, so the non-interference provisions are also about ensuring the safety of protesters and the crew of the vessels, amongst other considerations."
He said people were free to protest on the basis that they did not interfere with lawful, permitted activities.
"In the past there have been waterborne protests that have not interfered with any vessels and maintained the required distance."
