Someone else had the same question on 9/25 "I need help getting rid of lice fast", so I am just re-posting my answer for you. You may want to go back and look at the rest of the suggestions on that post as well.
Lice are one of the hardest, most aggravating bugs to get rid of. We've had it twice in my house. Lice cannot live long off the body, so wash what you can in very hot water, and all the rest-pillows, blankets, comforters, stuffed animals, hats-just put them in plastic bags for two weeks. Mayonaise is the gentlest on your head, you can use it over and over, is effective, and it is also, thankfully, the cheapest option. You must use real mayonaise, not the miracle whip or other "light" type. Generic is fine. Thickly coat all of their hair, slathering it especially around the ears and close to the nape of the neck, and any other place you saw a lot of nits. Cover with a shower cap. Keep it on for at least an hour. Use one of the good, metal nit combs, not those cheap plastic crappy ones that come in the box with the Rid. Those don't work very well. If you try to comb through with the mayonaise still in the hair, you won't be able to see the nits, so shampoo her hair before you start combing with the nit comb. Start at one side of the head, and work towards the other, using clean hair clips to keep the "clean" (already gone through) hair away from the "dirty" (not gone through yet) hair. After every pass through the hair, wipe the comb off on a towel to remove all the nits. This prevents a stray nit from being transferred back to the hair. You will have to go through the hair in very small sections(about a 1/3 of an inch by about 1- 1/2 inches), and probably go over each section several times to make sure all the nits are removed from that section before you move on. This will take hours to do, so you may want to rent a couple fun movies for your kids to distract them. You can either buy the spray to treat your upholstered furniture, or just put a clean sheet over them, and just change the sheet often until you know the lice are gone. Clean all the combs and any other hair accessories-I boiled my nit comb so I knew it was clean. Check through their hair with the nit comb every day until you are sure that all the lice and nits are gone. It is hard to get every last one even with the most diligent effort, so keep checking. As long as you get the nits before they hatch, you are okay. Keep looking for bugs as well, and retreat with the mayo each time you see them. Make sure you have someone keep checking your hair, your husband, your ex, and everyone else in the family. Your ex will have to be as diligent as you are, or it won't go away. Is there any way you can get him to agree to you keeping the girls for a couple weeks while you all work on this? That would limit possible "re-contamination". That way you would know the girls are getting checked everyday, and that their bedding isn't reinfesting them. Good luck to you. Don't give up. This will work, and you'll get your life back.