In A-mode, you fix the aperture for all of the multiple shots. When I say to spin the exposure I am referring to the exposure compensation button on the top of the camera and the spin part is the rear command dial. The setting here determines the base exposure for the 3 shot bracket and the bracket feature then varies the shutter speed to under expose, normal expose and over expose.
Don't change the aperture as the perspective will vary. Don't change the ISO as you will introduce more noise than you want. Don't change the zoom. Don't change the focus point and instead lock it in, you're on a tripod shooting a landscape, right?