While at Auckland University, he had met his future wife, Suliana Kaloumaira, a native of Moturiki Island.
A native of Moturiki Island in the Lomaiviti archipelago, Siwatibau was married to the late academic leader and former Vice-Chancellor of the University of the South Pacific, Savenaca Siwatibau, from 1966 till his death in 2003.
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Siwatibau led a group called Concerned Mothers Group Against the Bill in opposition to controversial legislation proposed by the government of Laisenia Qarase in early 2005, to make provision for amnesty to be granted to persons convicted of involvement in the coup of 2000.