Please explain Jack's new face and tell me the names are the twins now called in "Lord of the Flies"?
The twins are named Sam and Eric but because they are always together and even finish one another's sentences, they become known on the island as “Samneric.” Samneric are one of the final holdouts against Jack's power, but they eventually submit after being tied up and tortured by Roger.
Jack's "new face," as you call it, is the result of Jack masking his face with paint. Jack's painting of his face is a pivotal moment in his transformation from British chorister boy to savage, as the narrator informs us that "the mask was a thing on its own, behind which Jack hid, liberated from shame and self-consciousness." The savage authority of the mask also "compels" the other boys to follow Jack's lead, even though they did not elect him to be chief.
Sam and Eric's names have been slurred together to become Samneric. It is as if each has lost his separate identity and they are known only as part of a pair. Actually, most of the boys have lost their original identities and have descended into savagery. For instance, Jack has begun to paint his face, which shows the emergence of his inner beast. He smears his face with the blood of his kill as well as the juice of mashed plants, showing just how savage he has become. When Simon says, "Maybe there is no beast, maybe it's just us", he is prophetic in that statement. The beast within did more to destroy the boys than any physical beast on the island.