Is it appropriate to share the teachings or instructions one receives from a Guru with other people, according to Chapter 18?

Yes, Chapter 18 strongly advocates for sharing the Guru's teachings. While it acknowledges the opinion of some that what a Guru tells one person should not be told to others, it dismisses this idea as "merely imaginary and a meaningless fuss." The chapter explicitly states that not only direct instructions but even those received in dreams should be shared with all for their enlightenment. To support this, it provides the example of the sage Budhakaushika, who narrated the dream-vision of the Ram Raksha initiation to everyone. The Guru is compared to rain clouds, showering bliss on all without distinction.