Islands apart from PHI PHI?

I would forget about Phuket and Koh Phi Phi and go to the east coast about 3 to 4 hours drive from Bangkok at Koh Chang and Koh Samed. I think your parents will like it best and it's not that far from Bangkok. You could also go to Koh Chang and spend a few days then a boat to Koh Samed before returning to Bangkok.