Hii Sarvjit!

The practical exams as well as the Board exams for all the students of CBSE 12th class including the private Candidates; exams are held as per the dates alloted by CBSE. The practical exams are always held before the commencement of board exams. So, tell your brother to be in touch with the school authority through which he has registered for the exams. They will tell him the dates alloted to the school for practical exams of the Different subjects.

Hope you understand.

Good luck!