The Jewish father of three sexual abuse victims says that being branded an informer on fellow Jews to secular authorities is a taboo as frowned upon as incest.

Three of Zephaniah Waks' 17 children were abused by employees of Jewish institution Yeshivah Melbourne as students of Yeshivah College, including prominent Jewish victims' advocate Manny Waks.

Manny Waks and his team including his Dad Zephaniah Waks (right) arriving at the County Court, Melbourne, where he's appearing at the Royal Commission into child abuse. Credit:Penny Stephens

Mr Waks, who has been ostracised by the ultra Orthodox Chabad community after supporting Manny in going public with his story, likened the stigma associated with being a "moser" in the Jewish community to incest in general society "It's that bad," he told the Royal Commission into child sexual abuse on Tuesday.

Victims' families tearfully recounted to the commission how they had been shunned for reporting abuse to the police, which was seen as a breach of "mersirah" a religious rule preventing Jews from informing on other Jews to secular authorities.