Ideally the best way would be to remove the alloys and have full access to the rear or drum of the wheel.
They sound quite bad therefore I can highly recommend getting yourself some Car Pro Iron X which breaks down the old hard break dust and if required Valet Pro Bilberry wheel cleaner. The wheel cleaner can de diluted to various ratios depending on how bad the job is, although generally 4:1 is sufficient.
Once the wheels re clean get them protected using something like Chemical Guys Wheel guard or even Chemical Guys Jetseal 109 which can also be used on the paintwork.
If your unable to get the alloys off then a long reach wheel brush such as we stock from Vikan is very good to get behind and give it a good scrub lol, the above products still also apply