A better way would be to draw using strokes (Pencil tool). You may set the desired pencil mode and smoothness as per your need. Once you have drawn, its easy to make the corrections with strokes. Finally if you wish to convert them to brush fills, simply Select all the strokes and goto Modify Menu > Shape > Convert lines to fills.
If you still wish to modify your brush strokes, use sub-selection tool. Select the area you wish to modify (the anchor points present within the selection rectangle get selected.) Now use keyboard arrows to move the selected anchors around in sync with each other.
Hope this helps!
-Nipun