The train guards are the ones who check the tickets, do the announcements etc. the drivers went on strike a few years ago (and maybe partially now too?) to stop them being fired. They can't run trains without them.

If the law is anything like what we have in France, the inspectors are indeed allowed to strike. Which means, not showing up to work. If they are not striking they have to do their job.

And refusing to inspect tickets in this situation would be grounds for termination for "serious misconduct", because it's an explicit breach of their contract, and also a crime if the company says it has cost them more than 1000€ (not sure about the sum but you get the idea) because it would be considered as defrauding the company

It's the drivers who are striking.