Are the seats cloth ? If so, the rubber brush (which you can also get at a Petsmart store) will help move the hair over, allow you to gather it all in one place and then vacuum it all out. You need to learn how to make the brush work, its not just hammering on it, its firmly and sometimes gently, moving the hair from one end to the other for pick up..
If the seats are cloth and the dang dog was wet, well now the dog smell is embedded into the cloth and into the foam below. Harder to remove. May be impossible to remove all of it.
I would get a good odor removing soap for cloth, Chemical Guys has a "Fabric Clean" product that works pretty good and helps with the smell, but the only way to really get rid of the smell is to totally remove it.. It could come back if not removed..
I have used my VX5000 Steamer and Mytee HP60 Extractor on Cloth Seats and this works good for removing embedded dirt and crap out. You have to be careful that you don't compromise the cloth by tearing it, etc.,..
Don't forget the crease area between the top seat and the bottom seat -get all the way between the two really good..
Something else that sometimes helps is Meguiars Odor Eliminator spray...
The Pumice rocks for dog hair work pretty good - perhaps better on carpeting and not on the less stout seat material. Experiment carefully.. I have them too but always try the rubber tipped brush first.
Dont wet anything too much especially the seat foam. I have found some seat foams as in BMW's to really suck up water deep into them and hold it. It is killer hard to get all the water out of this type of foam. Ask me how I know..
It is always so much easier to wet and soak things down than to remove all that moisture afterwards.. Try to keep this in balance. If you have hot weather all of this will be easier with higher temps helping dry stuff out.. Fans also help dry the area quicker...
Good Luck with this !
Dan F