In reply to lewisday66:
Assuming you have led those sports routes, know how to safely descend again and your brother is a competent belayer for both these scenarios then you should be fine but obviously I don't actually know your skill and knowledge levels.
Whilst there is some single pitch and first pitch only stuff, ( plenty to keep you occupied ), the multi pitch sport routes are generally much better. Obviously you don't have to do the massive alpine / trad routes. There are some cliffs ( ecoles d'escalades ) where it is possible to train / practice your multi pitch sports skills. Many of the low level / valley crags have very generous bolting ( but not for every route so be cautious and check the guidebook ). Some of the higher multi pitch sport routes can have sections that are sparsely bolted - usually the 'easier' pitches.
A look at the Rockfax guide is a reasonable place to start, or 'Crag Climbs in Chamonix'. August can get very hot during the day - rock too hot to touch sometimes - and afternoon storms are common. Venues can also get very busy. However, by choosing shady times or climbing early in the morning, having a break and then again in the evening you can get loads done.
If your heart is set on Chamonix there is plenty to do. However, as others have said, other venues will have more stable weather, a lot more VFs and more single pitch that would probably suit you better.