Please follow following steps: Firstly, He is overweight, should reduce fat. Secondly, if he has frequent attacks of Sore throat or cold, he may be having an obstruction in the airway which should be treated eg Deviated Nasal Septum, Adenoids, nasopharyngitis. If so, an ENT specialist is the best doctor. Thirdly, he should get into the habit of sleeping on one side rather than . on the back. There are Nosnore devices or Snorepin/clips available on line which can be tried.
Next Steps
For his obesity, I can help on line, please see my profile.