Hey!

first you need to complete your undergraduation with science as main subject,then go for masters degree in any kind of specialization in which you are interested and then you can do PhD in the subject in which you want to do research. And side by side you can apply for positions in CSIR. Kindly note ISRO and DRDO will not welcome you easily until you are an engineer.

and yes, your 10th and 12th marks will affect your career, specially 12th classmarks as it the foundation to get admission in any of the universities.

Hope i answered your query.

Thankyou