Hello, to become an Astrophysicist please focus on Physics and Math in 10 plus 2 and as you said, you can aim for a dual degree in Astrophysics or Astronomy at IIST Trivandrum via JEE Advanced. Build skills in programming and research, and you can also do internships at institutes like IUCAA, or TIFR, and pursue a PhD in Astrophysics for a research career. There are many ways leading to your destiny, choose wisely. All the best!