Dear ( sibling's name)
hi! how are you ? i hope you are fine
i heard your competetive exams have started. you should work hard. remember work hard and score good marks this secssion i will see your report card and this time in all subjects it should be A1 no B's .if you have anyproblem ask help. still don't understand ask me.
do well in exams . convey your regards to everyone.