Ouch! Yes, you should be due some compensation if the Flydubai agent was in error (which it sounds like he/she was since Emirates allowed your family to travel.) The passenger is responsible for knowing the visa rules but the airline will face fines if they allow a passenger to travel without appropriate documentation. The rules should be clearly stated in the computer that the ticket agent is looking at. So write to Customer Service at Flydubai and ask them if their own rules were followed, if these rules are correct and if NOT, then ask for your ticket price back and the difference between your original tickets and the new ones you purchased. I wish you luck.