It’s a clever legal strategy. For political reasons, none of the frum schools will let him in (or rather, will let his kids in). So he is making legal mischief for them. It seems that the American style of using litigation as “warfare by other means” is spreading to Europe.
It isn’t clear why he doesn’t want to send his children to the Satmar schools (perhaps he has higher academic standards), or why he doesn’t home school. However this suggests the law suits are a deliberate nuisance against the non-zionist and pro-zionists, and is probably retaliation for their (arguably justifiable, and certainly predictable) harassment of him.
I’m surprised the schools didn’t try to have him summoned by the Satmar Beis Din, which he would have trouble ignoring. Of course, that would also be politically incorrect, especially for the zionist schools he’s been suing.