Thulsie brothers back in court for bail hearing
The duo was arrested during raids in Newclare and Azaadville last month and face three counts of contravening the Protection of Constitutional Democracy Against Terrorist and Related Activities Act.
Both are currently in custody.
On Monday, Magistrate Pieter du Plessis declared that the twins' arrest was lawfully executed by police officers, and that items recovered during the execution of search warrants "certainly indicated interest" in organisations associated with terrorism.
He said that one of the alleged suspects, Renaldo Smit, had indicated that he would testify and had given enough information to police to execute an arrest.
"Suspicions, together with confirmation of the witness, would in the court's view be sufficient to have reasonable suspicion of offense."
Du Plessis said the fact that the twins were strip-searched twice while attempting to leave the country also played a part in his decision.
Defence lawyer Anneline van den Heever said she would file an urgent application to the High Court to attempt to have the arrest declared unlawful.
She had earlier argued that her clients had been arrested on "far-fetched allegations".