The 25-year-olds, originally from Haryana state, in northern India, on Friday successfully climbed to the summit of Mt Cook, New Zealand's highest mountain.
They are believed to be the first twins to reach the 3724m summit and can now add it to an impressive list of mountaineering achievements.
In May 2013, they entered the Guinness Book of World Records after becoming the first twins to climb Mt Everest.
On Friday the siblings climbed Mt Cook in 14 and a-half hours - an impressive feat considering they only began training in earnest about a month ago.
Nungshi told the Otago Daily Times they had initially planned to attempt the ascent last year while they were studying at the Southern Institute of Technology in Invercargill.
However, trying to balance their studies and find time to train proved too difficult, so they delayed their attempt for a year.
They returned to India in July but quickly became too busy to train properly, so travelled to Wanaka about a month ago to focus on building their endurance.
''One of the most important [aspects] about training for Mt Cook is the endurance - if we could do 18 hours weekly, that's fantastic,'' she said.
''We did a couple of the trails here. We went to Mt Roy and Mt Iron [running] really fast with backpacks, pretty much running up and down.''
Nungshi said she and her sister went to the Plateau Hut with Wanaka-based guiding company Aspiring Guides on November 30 and had a very narrow weather window in which to complete the climb.
''It was definitely technically one of the toughest expeditions we've been on,'' she said.
''As compared to the Seven Summits it was a really tough mountain - usually we say you need to go to [Mt] Cook to train for the Seven Summits.
''But, I guess it's ideal if you do the Seven Summits and then come to Mt Cook.''
Reaching the ''pretty windy'' summit was a ''fantastic'' feeling, Nungshi said.
While the pair will return to India to focus on their NungshiTashi Foundation, which aims to advance the lives of Indian women and girls through the outdoors, adventure sports and mountaineering, they also have plans to return to New Zealand to continue their studies, aiming to pursue a master's in sports and exercise ''somewhere down south, probably''.
''Adventure will probably guide a large part of our lives ... we'd definitely love to come back to the [Mt] Cook region and check out some more peaks while we can and see how that goes.''
