What's your brother using to sand it? A DA power sander is fast, but won't always get it smooth, and it may be necessary to remove all the old paint and start from scratch. A DA sander with coarse enough disks WILL remove the old paint, which may be the best approach. The multiple layers of paint probably have different hardness and the transition between layers may always show up, although priming and block sanding will eventually cover those up. Once it has primer on it, a long block for hand sanding is the way to go.
