First the passenger should contact the airline and seek reimbursement of any expenses incurred.
If the airline rejects the claim, or ignores it, then the NEB should be contacted. It is best to contact the NEB of the country of the airline, although NEBs in the country of residence, country of flight origin, country of flight destination should also be able to assist, but there will be language/translation issues.
More information here:
How to Complain (but ignore the bit that tells you to complain to the NEB of the country where the incident occurred, follow my advice above)
This incident was a flight cancellation, the passengers likely are entitled to cash compensation of €250, in addition to refund of any expenses incurred for 'care'.