We had a difficult time mounting this bracket; we ended up having to use an extension bit. It was quite difficult. We also had to drill a hole in the top of the bracket itself to mount the back of the shelf to the bracket.
If I recall (it's been over a year since I installed them) I held the bracket up on the wall and marked the hole location for the upper hole with a pencil. Drive the screw in almost all the way so you can hang the bracket on it and slide it down onto the slot in the hole. Then you can plumb it up and drill the bottom hole, drive the screw, and then tighten the upper screw with a screwdriver.
One fastener is all that’s required. All the weight is on the vertical bar. You can attach with a screw or clear caulk.
The largest size available in the Oak Park design is the 8" bracket. It accommodates shelves from 8" to 12" deep.
In short, no. You would need to use a bracket that is at minimum 10 inches to support the shelf. In fact, using an 11.75 inch bracket would be the best solution, especially if you use the shelves frequently or store heavy items on them.
The depth needs to be 8 to 10 inches for a proper fit.