We hiked along the trail, by the stream, then went straight up a wash until we were just below South Sister. We then summited South Sister. We enjoyed the views for about 30 minutes then traversed down and towards North Sister. There were some challenging sections but nothing too extravagent.
We then summited North Sister, took a nice break. We then went to the NW side of North Sister and started traversing down. We ended up taking this wash all the way down to the trail. It was about 1700 feet of elevation loss and it only took 50 minutes.