I've got to be quick and will post more detailed information later, but the basic steps you need to take are:
1) Defend your home:
Create "defensible space" through landscaping and avoiding fire hazards.
Take special care to defend highly-flammable items, such as hay, so that the fire cannot spread to them easily, and so that if an ember (they can travel up to a mile) catches them on fire, it won't spread.
Use fire-resistent fencing and structures if at all possible, such as metal panels and especially roofs.
2) Have a plan:
Do you have heat-resistant and fire-safe halters? (They have to be made of natural animal products like leather or wool, or they will melt!)
Can your horses load quickly?
If you don't have enough trailer space for your horses, what will you do? Can a neighbor pick them up? Do you have a large "fire-safe" area you can leave them in and hope for the best, like a sand arena, dry-lot, or overgrazed pasture?
Where will you take your horses?
How will someone identify them if they need to? (You won't want to leave tack on in case they get caught - writing your phone number on their hoof is the recommended plan of action by BLM services)
If at all possible, DO NOT just turn your horses loose! The majority of people will not know what to do with scared horses!
I'll explain more later, but those are the basics...