My Dear (Name),
I hope this letter finds you and the family in the best of health.
Diwali is on the 22nd of this month. I wish you and your whole family a very happy Diwali.
I advise you to celebrate Diwali without crackers. Bursting of crackers creates a lot of noise and air pollution. Crackers are also a waste of hard-earned money.
Pay my regards to uncle and aunt.