Nick Thorkelson is Peter's brother. He is an artist in his own right-link
They grew up together, etc.
Most recently (Feb/March 2013), they worked on "Good Person of Setzuan" written by Bertolt Brecht & adapted by Tony Kushner.
In 2018 he was a special guest on Peters new album "Relax Your Mind". A tribute to the music of Lead Belly.