The families, all of whom had mentally disabled relatives at private residential care homes, run by Longcare Ltd, in Buckinghamshire, are also worried that they will never get to see the inquiry's full report.
Buckinghamshire County Council has promised they will be published. But the families fear that the authority's insurers will raise objections, as happened with an abuse investigation in Clwyd, North Wales.
At a meeting this week, they decided they would seek further reassurances before handing over documents they have gathered as background to the case.
Three staff were convicted earlier this year of ill-treating and neglecting residents. Gordon Rowe, who set up the homes, killed himself the day before he would have been charged with offences including raping residents.
The families believe Buckinghamshire, which registered Gordon Rowe as a home-owner, should have done more to detect the abuse earlier. But the inquiry's terms of reference do not include any investigation of the decision to register him.
At least 35 former residents are preparing to sue the council and 10 have already received legal aid certificates. June Raybaud, whose niece was a resident, said they should consider reserving their information to pursue the civil legal action.
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