Who is Laibele from The Cage and what is their importance?

Laibele is Riva's younger brother, he contracted tuberculosis as a child and never recovered, dying at age thirteen. Laibele was very close to Riva because of his illness. He was a kind and loving child, a fact that Riva said was true of all three of her younger brothers. Laibele had a difficult time of it, more so than some of the others, because he was stuck at home early into his illness while his mother and the three remaining of his siblings were at work. Riva was moved by his patience and she noted that Laibele wanted nothing more than to have the comforting touch of his mother while he was sick.