Complex sentence: The artists have chosen to exercise their copyright to control commercial use of Troll images, however, postcards, beer, and other products approved by the artists are commercially available and use is free to non-profit organizations.
Split into simpler sentences: The artists have chosen to exercise their copyright to control commercial use of Troll images. Postcards, beer, and other products approved by the artists are commercially available, and use is free to non-profit organizations.