Don't do this to your brother, but IF you end up in guard, and the guy donates both his arms to your cause, the arm bar advice is great, and if the arms are straight a standard triangle works well. If your legs are flexible enough, you can go for the double arm bar.
What I personally normally do (and I dont advise it unless your throat is really stout!) is pick an arm and pull it towards me even stronger. My throat can handle a ton of pressure, so it doesnt bother me at all. It makes a nice "thumb lock" by hyperextending it. It's a great surprise move, but again unless you've conditioned your body for it I wouldn't advise it!