Go down to the relay and disconnect the low voltage wire from the dasboard switch. Wire up a 12 volt lamp and turn on the switch. If the lamp lights, it is not the switch. Connect the fans (one at a time) to a 12V souce to see if they work. If they do, you need a new relay. If they don't, you need new fans and possibly more.
Here is an excellent 12 inch replacement fan that pulls way more air than the stock fan at a lower amperage draw,
PermaCool 18122