Kevin Winter/Getty ImagesJanet Jackson and a couple of her siblings refuse to back down from their claim that the signature on their brother Michael's will was forged.

In a statement released on behalf of Janet, Randy and Rebbie late Friday, the siblings continue to question the validity of the will. Furthermore, they claim, "The negative media campaign generated by the executors and their agents has been relentless. In recent weeks, the media received preposterous reports -- all now proven to be false -- of a purported kidnapping of Katherine Jackson and of physical and verbal abuse of a child."

TMZ.com last week published -- then retracted -- a story claiming Janet slapped Michael's daughter, Paris.

The siblings also allege they were barred from visiting their mother, Katherine, and Michael's kids in an attempt to "damage fundamental family relationships" and "isolate Katherine Jackson from anyone questioning the validity of Michael's will."

In bold print, the statement says the siblings "stand to gain nothing financially" by contesting the validity of the will.

Last week, a Los Angeles judge reinstated Katherine as the guardian of Michael's three children: Prince, Paris and Blanket.  The kids' cousin, TJ, is serving as a co-guardian.

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