Why is he apearing in the court since his father took all the blame ?
His father's explanation is not a juristic act. Any information on this issue needs to be collected and looked into in that hearing with a judge present, otherwise it's juristically irrelevant. He could announce all kinds of things, but of course, that can't be taken as evidence in the matter.
It's nothing to worry about though, this hearing couldn't be avoided by any means and actually is the necessary step in order to be cleared of any accusations.
As things stand, this probably won't go to court, seeing as this is probably a case of tax negligence and
not tax fraud. But that depends on the evidence. In the worst case, his father might be put on trial.