How can we know the authenticity of the teachings of saints like Sant Dnyaneshwar and Samartha Ramdas Swami?

From: Vivek Kulkarni

Are the teachings of Samartha Ramdas Swami (the Spiritual Guide of Shivaji maharaj) authentic? Is there any “parampara” system he comes in?

Did Sant Dnyaneshwar accept dvaita vad or advaita vad? The Varkaris in Maharashtra clearly worship Krishna, but I dont know about the philosophy.