Its unnecessary for you to fill both the examination as you will get the chance to go for NCBS through TIFR GS only. Now you can apply for JGEEBILS. The examination only focuses on NCBS and you may get a edge to your subject if in sudden way TIFR GS get less good than JGEEBILS or the converse happens, you will get the chance to get in NCBS.

To know more about JGEEBILS visit the link below:

https://www.careers360.com/news/9515-JGEEBILS

To know more about TIFR GS visit the link below:

https://www.careers360.com/university/tata-institute-of-fundamental-research-mumbai

I hope this answer helps. All the very best for your future endeavors!