Need some basic diagnostic info to isolate the problem to a likely cause. Is there power to the non-working fans? If no, you need to troubleshoot the 12v supply lines and grounds. If yes, troubleshoot the fan units themselves. If a 12v supply problem, do all the fans share the same 12v power lines, or are they separate? The fact that one quit before the other two suggests separate. Do the fan units have remote wall switches for on/off? Do they have the optional wall control panel that lets you change fan speed, rain sensor, etc. And what model of Fantastic are they?
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC