Paragraphs help. Your text is a disorganized mess. Is there a question in there?
Koh Chang is boring and isolated, the boy would probably prefer Hua Hin where he could be a little more independent,
For beaches, the Phuket/Krabi area wins easily. Plenty of beach villas south of Patong. For euro-feel Koh Samui also has many small villas available but the food is bland.