One of my dogs has walking dandruff..the Cheyletiellosis mites,absolutely horrified but i have to treat all of dogs,i have 5 and 1 is 5 weeks pregnant..what  can i treat her with? Any advce appreciated.

Frontline spray I found better than spot on for this mite and is apparantly safe for pregnant bitches

If you don't want to use chemicals you could try Dawn liquid soap (diluted).  A full bath with it being left on just a few minutes is sufficient to kill mites and fleas.  This is what it says about it "Dawn dish soap kills fleas and in two ways. The first way is that it strips the fleas of their wax coat making their exoskeletons vulnerable. The second way dish soap is effective at killing fleas is that it changes the surface tension of water so they sink."  I have not used it yet but will at the first sign of harvest mites which my dogs had last year and I am hoping that it rids them in one go.    Read up on it if you are interested, don't use too often as it will dry skin although you can condition afterwards and it will affect effectivity of spot on flea treatments so don't put one on within 48 hours I think I read.

I agree with bucksmum.  I've used Frontline spray on a pregnant bitch with no ill effects.