"It's been an honour and a privilege to have worked for the All Blacks over the last few years and to help the team achieve its goals, including winning the Rugby World Cup, and I look forward to getting stuck into next season after the summer break," Foster said.
There had been speculation Cron might finish as forwards coach but has committed to another two years.
"I'm really enjoying the environment and the next couple of years will be an exciting challenge for the coaching team as we look to identify talent and help develop them into world-class rugby players," Cron said.
Hansen has said he's likely to step down as All Blacks coach after the 2017 season, when the British and Irish Lions tour.
Wales will tour New Zealand in June for three tests which is followed by the annual Rugby Championship and the end-of-year-tour to Europe. The All Blacks are expected to play Ireland in Chicago on their way to Europe at the end of 2016.
Hansen has clearly found a winning formula and welcomed the re-signing of his support staff.
"It's great news for New Zealand Rugby and myself to have these two world-leading coaches sign back on with the All Blacks," he said. "They have both played a major part in making this team what it is. They understand the culture and what's required in the Test arena to make a team successful, and will be vital in making sure that we continue to grow our game in the years ahead."
Sopoaga has played 49 games for the Highlanders and made his All Blacks test debut this year against the Springboks in South Africa.
The 24-year-old currently holds the season record for points scored by a Highlander with 191 in 2015 and is the second-ranked Highlander for most career points on 453 (behind current assistant coach Tony Brown).
"I'm so grateful for the opportunity to sign to the Highlanders until 2018. I owe a lot to the coaching staff and the organisation for sticking by me and allowing me to develop, not only as a player but as a person. I wouldn't be where I am today without the great team culture, teammates, coaches and medical staff. I'm looking forward to my future with the club," Sopoaga said.
Sopoaga is likely to feature more regularly for the All Blacks next season after the retirement from international rugby of Dan Carter.