Could you provide a comprehensive list of all the Guru biographies and their authors that are identified in the preface?

Certainly. Chapter 0 of the preface mentions several distinct Guru biographies. These include: the famous 'Brihad Guru Charitra' by Shri Saraswati Gangadhar; a detailed and scholarly biography by Shri Samarth Sadguru Tembhe Swami, also known as Vasudevanand Saraswati Maharaj; and an unprinted biography by Shri Samarth Sadguru Dattatreya Maharaj of Balekundri. Additionally, it references two short but graceful biographies of Shri Sai Baba written by Shri Dasganu Maharaj, which are parts of his 'Bhaktalilamrut' and 'Bhaktisaramrut'. Finally, the text describes the 'Laghu Guru Charitra,' a separate and much older work of 707 verses, distinct from Saraswati Gangadhar's more famous book.