Yes, you will be eligible for JOSAA 2025 if you meet the following criteria:

1. Pass the NIOS board exams in April 2025: You must pass the three subjects you choose from the NIOS board.
2. Achieve a minimum required score in JEE Main: You will need to score the minimum required marks in JEE Main to be eligible for JOSAA counseling.
3. Have Physics, Chemistry, and Mathematics as your main subjects: These subjects are mandatory for JEE Main and JOSAA counseling.

Regarding the highest individual marks for 5 subjects, JOSAA considers the best five subjects from your qualifying exam. This means that your NIOS board marks will be considered along with your ISC board marks to determine your overall percentage.

Therefore, you can use the marks from both your ISC board and NIOS board exams to calculate your overall percentage and determine your eligibility for JOSAA counseling.