Alison Lewis, who was arrested after the bodies of her lover Mandy Power and Ms Power's family were discovered, had earlier spoken of her intention to sue the force.
Her ex-husband Stephen and his brother, Acting Inspector Stuart Lewis, have also begun action for wrongful arrest.
Newspaper reports have claimed that Mrs Lewis is seeking £250,000 in damages and the brothers want £1m each.
But Ms Lewis' solicitor Bernard de Maid could not confirm the amounts in question.
The Lewis brothers are still suspended from the force and are being investigated on disciplinary matters.
David Morris, 40, was convicted of killing Mandy Power, her mother Doris Dawson and daughters Emily and Katie, and was jailed for life.
The family were battered to death when Morris embarked on an "orgy of savagery" in June 1999.
Shortly after the verdict was announced on Friday 26 June, South Wales Police force confirmed it had received notification that Mrs Lewis intended to claim damages.
Ms Lewis said the force had wrongly branded her a murderer.
"I feel I still need answers, and the only way for me to get those answers from South Wales Police is to sue them, because what happened on that day... has effectively ruined my life."
Poster campaign
During the case, the defence counsel had claimed the "probable" murderer of the Power family was Ms Lewis.
Last week, protest banners claiming Morris' innocence were taken down by council workmen in south Wales.
The signs, daubed with "Killer Walks Free", had been were hung from bridges over busy roads in the Dyfatty and Ravenhill areas of Swansea.
The horrific case has split the community, with other residents mounting their own poster campaign declaring support for relatives of the four victims.
On Monday, other supporters of the man convicted of the Clydach murders were told to stay away from the village by a community leader.
Campaigners were alleged to have visited pubs in the village on Saturday night in an attempt to get a petition signed in support of Morris, started by his former wife, Wendy.