He singled out the Holocaust Educational Trust, which Lord Janner founded, as "superb - like all the community bodies".
He also paid a warm tribute to his own rabbi, David Mason of Muswell Hill Synagogue, who had been a "brick". Mr Janner's sister, Rabbi Laura Janner-Klausner, senior rabbi of the Reform Movement, is said to have received strong support from both rabbinical and lay leaders in the movement.
Lord Janner, a former MP and prominent figure in the Jewish community, died in December 2015, aged 87, after suffering from severe dementia.
Some 33 people have made claims of historical sexual abuse against him, with the offences alleged to have taken place between 1955 and 1988. Lawyers for the alleged victims say their clients have been waiting years for justice.
Last year, Alison Saunders, the Director of Public Prosecutions, decided Lord Janner was too unwell to face prosecution, but the decision was overturned after a public outcry. A judge ruled that the peer should face a "trial of the facts", assessing the evidence but without delivering a verdict or sentence. Lord Janner died before it could take place.
The Janner siblings have strongly denied the claims against their father, but now, after months of silence, have come out fighting. Both Daniel, a barrister, and his other sister Marion, a mental health campaigner, have given television and press interviews for the first time.
Commenting on the family's decision to go on the offensive, Mr Janner said: "When the Director of Public Prosecutions announced her decision not to prosecute dad in April 2015, we were not surprised, but we were astonished by the outcry. We immediately put out a statement saying that he was entirely innocent, but we were caught in a media and national frenzy, and there was nothing more we could do".
Lord Janner appeared in court last August, accompanied by his daughter, Marion. Plainly unsure of what he was doing or where he was, the peer, in what became his last public appearance, just managed to agree with court officials that he was Lord Janner of Braunstone before leaving the courtroom after the briefest of appearances.
His son told the JC: "We were faced with criminal proceedings, where you can't say anything. But now, we can speak, based on solid evidence which we now have. Now is the right time for us to speak out."
Mr Janner explained that another reason for the family breaking their silence was the Goddard Inquiry, which was tasked in July 2014 by then Home Secretary Theresa May with investigating wider claims of child sex abuse.
"The inquiry has taken our father's [case] as a separate strand - he is the only named individual in the 13 separate lines of inquiry - all the rest are institutions. That is wholly obscene and wrong. He is not an institution and he has never been convicted".
The family had declined to become "core participants" in the Goddard Inquiry, because, Mr Janner explained, "that would be a manifestation of the witch-hunt frenzy" which surrounded the issue.
Besides, he said: "As core participants we would have no right or opportunity to cross-examine [witnesses]."
He accused the inquiry of "approaching this case [of allegations against Lord Janner] on the assumption of guilt. So how can there be fairness, not least when he is dead? We are having nothing to do with this obscenity".
It is understood that some of the "solid evidence" on which the family is relying is material unearthed by the Mail on Sunday. An article published last weekend claimed that the principal complainant against Lord Janner was a former children's home resident who had "made bogus claims that he was sexually abused by a woman at the care home where he lived".
Most of the 33 claimants who have made allegations against the peer are seeking civil damages from his estate.
Mr Janner said: "All the indications which we have are that those intending to sue have that as their motivation."
The family have repeatedly rejected the suggestion that an "Establishment cover-up" was a reason for the former MP not to have been charged in 1991, when the matter first surfaced. Rather, say the Janners, there was no evidence against him.
In an interview with the Sunday Times, Mr Janner revealed that Leicestershire Police had twice asked him if he had ever been sexually abused by his father. He said it was a "disgusting" claim which he utterly rejected, telling the police that he had had "a wonderful childhood" and that all three children had admired and loved their father.
