Your first language, also known as your mother tongue or native language (L1), is the language you learned naturally during early childhood. It's typically the language spoken in your home environment from birth.
The question states you were born and brought up in a village where everyone spoke Hindi. You started using Hindi without going to any school. This indicates that Hindi was the language you acquired naturally from your family and community during your earliest years.
This process clearly establishes Hindi as your first language based on how and when it was learned.
Later, you attended school and studied multiple languages, including English, Sanskrit, and Urdu. You also developed fluency in English. However, learning these languages in school represents formal education and secondary language acquisition (L2, L3, etc.).
Achieving fluency in a language like English later in life, while impressive, doesn't change the language you learned first during childhood. Your ability to speak English very fluently is a result of study and practice, not natural acquisition from birth.
Based on the information provided:
Therefore, your first language is Hindi.