John & Sarita Holzmann are the owners and primary writers of our curriculum materials. You can read about them at http://www.sonlight.com/who-are-we.html
The booklist for each Sonlight package is curated by the company’s founder, Sarita Holzmann. Sarita is a veteran homeschooler with 25 years of experience in curriculum development. Our curriculum authors have a variety of backgrounds and qualifications. Several are trained educators, others are veteran homeschool parents. All of the authors within the product development team work with Sarita to ensure that the content they write meets company standards for accuracy and usability.
I suspect the best "proof-test" for our curriculum materials would be to take a look at our latest Scholarship winners (http://www.sonlight.com/scholarship-winners-2014.html). You will find brief bios of this past year's winners at the link I've provided. Our scholarship program has been around for 10 years or more, and consists of students raised and educated with Sonlight programs.