I just saw a beagle that had just been rescued and its ears were covered with tiny ticks. I thought this was odd, but evidently either some ticks prefer the ears or it's just convenient for them (i.e. the ears are easy to hop on).
Give them some frontline and the ticks should start dropping off within about 24 hours.
A flea/tick 'dip' is the quickest way to do it, which is all a groomer would do (plus a good comb-out). The chemical at work is permethrin, its a general purpose insecticide that goes into many sprays, dips, and topical drops. Hopefully this isn't a house dog or you will have a much bigger problem on your hands than just the bugs currently on the dog...
Oh, and are you sure they aren't canine lice? They have a very similar M.O. but they are smaller than ticks and tend to stay in the hair instead of dropping off after they feed. Treatment is similar but you need to be more persistent since they cling more than other bugs. Fortunately, they die just as fast as any other bug when hit with permethrin.
They have hundreds? So they had a few at first but you didn't decide to do anything about it until it was hundreds? I'm just not seeing how they can have hundreds all at once, but I guess anythings possible.
I would take them to the groomer first and get them a special bath, wait 24 hours and then buy a product like frontline, or advantage which has been suggested.
Poor dogs they have to be uncomfortable, i'm glad your finding a solution to make them better.