How should the Jews respond to the antisemitic bus drivers who refused to transport them?

[Kruska]

Wrong. If they can prove that these drivers colluded to deny service to these people, they can sue. Breech of contract. All those drivers, if they called in sick, need to show doctors excuses and proof they went to see a doctor. If they don't have that, then they're in trouble. Bigly. The company is, for sure. To what degree the individual drivers would be responsible is unclear.

Nope,
those Jews/travelers can only sue the Bus company - due to non delivery/breach of contractual obligations, they cant sue the individual drivers. Since these two parties share no contractual obligations with each other. Furthermore an "obligation" for an employee to forward a MD's attest for sickness is individually regulated in the employment contract - e.g. more then 2 or 3 days sick-leave requires an MD certificate/attest.

A passenger can sue an airline - but not it's respective pilots, or e.g. its ground maintenance crew - for a cancelled flight.

The Bus company can evade the claim via - Force Majeure, e.g. sudden sickness of drivers, or e.g. a strike - lastly it depends on respective exclusion clauses, that might be stipulated in the Bus companies standard contractual terms.

If the Bus company decides to sue it's own staff is another issue. Usually they won't, since a MD's medical report/judgement is kind of Taboo.