The single best source of information about Fire Ants is Texas A & M, every other web site I've seen about them simply copies the materials from TAMU.
Chiggers can be a whole other problem. Sulfur is one of the products listed as a deterent, something to keep the wee buggers off you, not as something that can be spread around the yard to control them. Non of the material available to the average homeowner for chiger control is terribly safe, although for some reason some of the products available to licensed pesticide applicators are pyrethrin based.

Here is a link that might be useful: Fire Ant Control

I use a mosquito repellant spray on my white shoes and up my white socks. Makes it easier to see the ants if they get on me. My pant legs are tucked into my socks. So far, I've not been attacked. (I wouldn't want to test the spray by standing on an ant hill : ) Fireants are vicious!

You might try mixing ammonia and water at a 5:1 ratio.. 5-parts water.. for the ant problem... Ants hate ammonia and it kills on contact as well as in it's gas form when it evaporates... Fire ants may need a lower mix ratio, pos. 3:1, but start with the 5:1 and scale it up or down accordingly.

Fire ants are likely to wait until they've made it all the way up into your hair line before they begin to sting. That's when you find out they've been dropping down into your shirt by the scores.

Anyway, there's granular ant bait products on the market with Spinosad as the active ingredient. This is listed as organic and can be used in vegetable gardens and other food crops. I strongly recommend that you locate such a product and give it a try. Since the active ingredient is carried on a bait (like Amdro), it will be taken into the mound and spread around to all of the residents.

Because Spinosad is a very broad spectrum poison the OMRI people suggest very strict and limitied uses of this product.

Here is a link that might be useful: OMRI on Spinosad