Its dependent on the subject. For subjects like Biology, NCERT will be sufficient enough. But if you consider subject like Mathematics and Physics then NCERT may help you but you need to practice from other resources. Now if you consider chemistry then it can be really helpful in some parts such as Inorganic Chemistry but its not sufficient enough. So if you want you can study NCERT but for problem solving you need to practice from other resources.

To know about KVPY books visit:

https://school.careers360.com/articles/kvpy-books-know-best-books-for-preparation

I hope this helps.