freakin lice!! Dont know what else to do

so, we have been treating my poor chickens that have lice for several weeks now. they do not seem to go away. we repeat treat with the powder weekly and they have defently lessened but the poor chickens are still crawling with them. i have made sand bath with DE in it. i have cleaned the whole coop with bleach and dusted boxes and floor with DE. dont know what to do. it cant be good to keep covering the poor things with this chemical powder! i have ceder chips arround coop to deter bugs. we are at out withs end and its starting to get pretty cold for the ones with naked backs!

 

i have been using the poultry dust and the DE. i have treated both birds and surrounding areas. i havent tried frontline or the ivermectin. i dont use frontline even for my cats or dogs . its wicked expensive. i wonder if the tractor suply brand as i use for my house animals would work for them. would i havve to weit a week again before treatment or what?