Why are Gabriel and Roberto released in The Giver by Lois Lowry?
After spending his first night back in the Nurturing Center, Gabriel cried all night. He had been staying with Jonas's family in the hopes he would grow more quickly and so that Jonas's father could help him act like all the other babies and sleep through the night. The night crew "couldn't handle it" and so it was decided Gabriel would be released the next day.
Roberto was an old man who was released. Jonas had helped him with his feeding the last time he had volunteered at the House of Old. His friend, Fiona, had attended Roberto's release and explained the ritual for release. It is never stated why Roberto is released but you can infer it is because of his age.
Roberto was released because of his old age. At some point all elderly must be released. He might have been required to be released or he may have requested it himself.
Gabriel was not released however he would have been released, if Jonas did not take him on his journey to Elsewhere, because he was so restless at night.