why was Gabriel staying with Jonas's family unit?

Gabriel is not considered to be progressing as what the elders feel is "normal". Jonas's father gets to bring the child home to get it to cry and behave like a "normal" baby or else it has to be "released". When Jonas's father brings Gabriel home, Lily notes that the newchild has the same pale eyes as Jonas, which Jonas resents because society does not consider it polite to mention when an individual is somehow different from others.

Gabe stayed with the family because when he was first given a name as to though Jonas's father was a Nuturer, Jonas's father was to make him stop crying and act like one of them, or he was to be "realeased". In jonas's community, everyone lokked alike. Being different was not accepted in Jonas's community. Lily points out that Jonas and Gabe have the same colored eyes. Lily decides that it was okay to make fun of it and so she did. It was Impolite and rude to make such a gesture.