When I look toward Ko Lan from Jomtien Beach I see two smaller islands, one to the right of the big island and in front of it (the north end of Ko Lan is behind it, and another one further right. I can't find that one further right on google Earth. I don't have double vision.

depending upon your viewing location and direction, what about: Ko Sak?

+ 1 Ko Sak

From Google https://www.google.com/maps/@12.9299838,100.794418,15z

On google, looks like Ko Sak is behind the small island to the right of the northern tip of Ko Lan. In the photo, there's a distinct gap between the two small islands. Ko Sak view seems like it would be blocked by the small island (of the two small islands in the photo, the one on the left).

Viewpoint is same as intersection of Theppraya and Jomtien Second Road. The two smaller islands north and NE of Ko Lan seem lined up, so you shouldn't see a gap between them.

Can go by speedboat but not allowed stay overnight