While I guide for salmon at the North tip of Graham Island I cannot really tell you too much about the rivers. However, since no one has responded to your question I'll try to help as best I can.
The steelhead runs of the Charlottes are primarily winter and spring run, I know that the Lodge I work for - Langara Lodge operarates a steelhead lodge at Kumdis in the winter. As well, the rivers are spate rivers that are dramatically dependent on rainfall to provide fishable water levels. There are many stories of guys going to the Charlottes with great hopes of wild steelhead only to be completely thwarted by extreme low water conditions - it is kind of a crap shoot.
What is consistent and would probably be where your efforts should lie would be beach fishing for cutthroat and salmon. By early August there will be salmon all over the place and the cuts are always around. I'm sorry I can't really help you out as far as specific spots, but this could be a starting point for you, if you will have access to a car, check out a map and find a stream or river mouth and have at it! Good luck.