Sonya Rockhouse, who lost her son Ben in the 2010 tragedy, welcomed the support.
"Even though it's taken so long, it's good to know they've swung in behind us getting truth and justice.
"What's really great is this means it's the end of all the politics, and now it's about everybody doing the right thing by our men."
The Coalition Government and the Opposition have long fought over the viability of re-entering the mine's drift. The Labour-New Zealand First coalition agreement said they would "commit to re-entry to Pike River", while National has always said it was too dangerous to do so.
The families' group has not been shy about expressing its disappointment with the previous Government, not only about re-entry but also for feeling at arms' length from information about the mine and the decision-making process.
On the tragedy's eight anniversary last year, just days after the Government had announced that re-entry would proceed, the families were angered when National leader Simon Bridges said an apology wasn't necessary.
Bridges said at the time that the legacy of the 29 men who died had been honoured by the Royal Commission of Inquiry and changes to the health and safety laws.
Anna Osborne, who lost her husband Milton in the 2010 tragedy, told the Herald this week: "It's the will of the Government to help. There was no will in the past from the previous Government."
But after the meeting with Mitchell, the families' group was buoyed by National's support.
Mitchell said the families shared with him their view of the previous Government's failure.
"I'm not going to comment on the past. All l'm going to do is focus on the future. I'm really pleased they are engaging in a process that's positive for them.
"I wanted them to leave with a strong sense of the fact that we are behind them, that we do understand, that we do realise the stress and everything they've had to go through."
Mitchell will travel to the mine for the breaking of the 30m-seal at the entrance to the drift on May 3. Prime Minister Jacinda Ardern, Deputy Prime Minister Winston Peters and Pike River Recovery Minister Andrew Little will also be there.
Little welcomed National's support.
"It's good for the families to know that there's no politics in this."
He said the Government had tried to make the families a part of the re-entry process as much as possible.
"They've been involved, including in decision-making, every step of the way since we set up the Pike River Recovery Agency. It is as much their project as it is the Government's.
"Those families, and anybody who worked for Pike River caught up in the tragedy, have been badly let down by a whole heap of things: the company, the health and safety regime and the oversight provided by the Department of Labour at the time.
"This is what we are trying to put right. People have been let down totally unnecessarily, at the cost of 29 lives."
Winston Peters said in 2016 that he would be happy to be the first to re-enter the mine's drift, and he doubled down on that last year.
But Little said that won't be happening.
"He wanted to, but I think he realises now that the health and safety considerations mean that he won't be the first one in."
