CAT 99 only based on special offer.
You'll get CAT A ( subload ) and CAT C ( firm ) unlimited after 6 months.
as Thypoon said your relatives only got one of those CAT A and CAT C a year.
But they entitle for CAT 99 whenever there's an offer.. so keep checking! Usually they have it in notice board in CBC or emirates building. Every three months.
CAT 99 means the ticket cost you around 99 dollar and it's firm.