My grandfather filed a petition for us in 1996. He eventually dies and all of us are already over 21 years old and are married with children. In November 2024 our dad received a letter stating that the petition filed has been approved and US Department of State's National Visa Center(NVC) and we were given instructions for completing immigrant visa application. In the letter we were also notified that a visa number is already available. Does this means we are eligible to file application for immigrant visa?