The family moved from France when the twins were aged 14 after their parents fell in love with the country while on holiday.
"Our parents liked the lifestyle so much; it's much more peaceful than France," Cecilia said.
Having lived in the country for so long they felt "more Kiwi than French" and decided to gain citizenship to become "fully integrated".
They are both studying at the University of Otago and planned to go out for dinner last night to celebrate.
Mayor Peter Chin said it was one of the largest citizenship ceremonies the city had seen, with 36 people taking part.
No ceremony was held last month.
Others to swear allegiance were: Mousab Mohamed Soliman Arafat (Libya); Jennifer Mary Bannister (Britain); Aditi Bardhan (India); Marian Louise Baxter (Britain); Heather Mary Geraldine Chambers (Britain); Anne Kathrein De Castro (Germany); John Eteuati (Samoa); Graeme William Flottman (Australia); Rene Rudolf Gloor (Switzerland); Susan Frances Hamel (Britain/America); Anthony Derek Harland, Sarah Amanda Harland, Hannah Alexis Harland and Jack Alexander Harland (Britain); Edwin Wei Loong Khoo (Malaysia); Gayle Mallorie Mather (South Africa); Maira Muller (Brazil); Helen Anne Nortier (Britain); Hyun Hee Park and Yoon Young Jang (Korea); Se'u Pupualii, Kolopafaava Mikaele Pupualii, Peterpaul Mose Pupualii, Michael Pupualii and Simon Timordili Pupualii (Samoa); Krishna Reddy, Aruna Devi Reddy and Muni Deepika Reddy (Fiji); Tency Sabu, Sagar Sabu and Sarangi Sabu (India); Roshni Preet Kaur Rajinder Singh (Malaysia); Matheus Antonius Smits (the Netherlands); Elizabeth Diane Tyrell (Britain).
