Complex sentence: The makers referred to books such as "To Everest and Beyond" (by Edmund Hillary) and accounts of various other mountaineers, even meeting a few of them personally to ensure that they got the right facts.
Split into simpler sentences: The makers referred to books such as "To Everest and Beyond" (by Edmund Hillary) and accounts of various other mountaineers. They even met a few of them personally to ensure that they get the right facts.