This question was asked only nine days ago. (Not directed at you, OP) I think it needs to be in the FAQ.
Anyway, here's some answers.
What stopped the British Empire from invading Nepal and Bhutan when they had most of South Asia under control?
Why were Nepal and Bhutan separate from the Indian Empire?
As I understand, the Princely States in 1947 were given 3 options: join India, join Pakistan, or remain independent. Were Nepal, Bhutan, and Ceylon given those options as well or were they not expected to join either state?