Visit dentist for clinical examination and ultrasonic scaling. Kindly go through the blog mentioned in the link below. It will be helpful. Bad breath is related to lack of oral hygiene, systemic conditions (if any), medications (if any), mouth breathing, gastric regurgitation, dry mouth etc etc. Find the cause of bad breath with the help of doctor and treat it.

Due to poor oral hygiene. Should go for scaling and polishing. Opg xray to determine whether there are cavities or food lodgement is there,which needs to be filled

The tongue covered with white plaque could be the reason of his bad breath. Get professional cleaning of the mouth done and start using a tongue cleaner.  Ask him to drink plenty of water and keep himself hydrated. He will start to notice an improvement in a few days.