As LaMa said, You can’t use the same tactics here as in the US.
It is a criminal case of the Belgian state against Scientology and some of its members after an investigation asked for by several people. (Meaning suing those people won’t do anything for this case. )
First of, there is a difference in the charges of conducting criminal activities and being a criminal organisation. It’s almost certain the first kind of charges will be pressed, otherwise the prosecutor wouldn’t be recommending a trial.
Suing the Belgian federal government about this matter can’t be done inside Belgium at the moment because there already is a case (criminal practices). Scientology is not a forbidden group in Belgium (laws of religious freedom). Grounds for a case about discrimination are very small (but might be used in court defence).
NOTE of the author: Scientology claims there is a climate of intolerance and discrimination. However, while sects are frowned upon (and Scientology considered one), they are tolerated in Belgium as part of the strong public opinion about free speech.
They will have to wait until after the judge has come to a verdict at the Regional Court, then there can be one appeal at the court of appeal about the criminal charges, after that there is the Court of Cassation which can only judge whether no laws have been broken and no rights ignored. Here is the full version: Organisation of justice - Belgium (warning: legalese might cause insanity and/or a headache )
The option for a counterattack as I see it is to go for the religious freedom. After all, the European court for Human rights declared Scientology members to be able to practice their beliefs (5 april 2007). But again, this is a criminal case, and they still have to go trough the Court of Cassation before they are allowed to appeal with any European court.
However. This trail will be a very strong precedent, both in Belgium and Europe (and perhaps even internationally), no matter how it turns out. And, if Scientology is found guilty, inside Belgium in will be a very solid ground to make them a forbidden organisation, similar to the Hell’s Angels in Belgium and Germany. Either as a judgment in this case or as a separate trial.
We’re in for a couple of years of news about this.