Who are the only biguns who remain with Ralph?
In Golding's Lord of the Flies, the society that emerges on the island is a mix of civilized and savage traits. This is suggested in some of the language the boys use; for example, terms like "littlun" and "bigun" become true nouns. Littluns are the younger boys (little ones) and biguns are the older boys (biguns), ranging from around 6 years old to 12.
This distinction is important in terms of the book's commentary on society. The littluns are basically helpless; they were ostensibly supposed to be protected and cared for by the biguns. However they eventually degenerate into playing aimlessly all day, with no responsibilities. The biguns, then, hold even more power and responsibility, and a bigun is "worth" something on the island. Having the support of the other biguns is the primary focus of the power struggle between Ralph and Jack.
Eventually, Jack's combination of sadism and hedonism either convince or terrify most of the biguns into joining him and rejecting Ralph and the power of the conch, and with it the civilized behaviors and rule of law that the conch represents. By Chapter 10, only three biguns remain with Ralph; Piggy, and Samneric. Piggy remains because he knows that Jack hates him, and will try to hurt him if he can; he needs Ralph's protection. Samneric function more transparently as symbols of the general population; as twins, they represent uniformity and monotony, and their actions, such as following Ralph but failing to maintain the fire, point to their willingness to be led but their inability to self-motivate.