Complex sentence: It was founded by a group of enthusiasts interested in the preservation of the site and history of The Crystal Palace, and have been behind a number of suggested proposals for the site, including the successful establishment of a museum.
Split into simpler sentences: It was founded by a group of enthusiasts interested in the preservation of the site and history of The Crystal Palace. They have been behind a number of sugested proposals for the site, including the successful establishment of a museum.