The Saengchan family was a minor branch of the 3rd elite family in Bangkok. These are always called 'Side branches' among the elites.
The family had four siblings; Two boys and two girls. Kaew was the last born while her elder sister, Sirikit, was the second born. Maybe because they were both girls, these two were very close.
It happened that Kaew's mother was the best friend of King's mother, and because of this, the four kids of the Saengchan and the two kids of the Dæd-Câds spent a lot of time together while growing up. Their mothers took them everywhere together. Because of this, King and Sirikit, generally referred to as 'Siri', — grew up together as friends.