Do you mean at Publish > Family Group Sheet?

Or the Family View in the People Workspace?

Neither one shows siblings of the selected person as a parent - nor should it. The family is defined as the nuclear family - parents and children. Not the parents, plus the parents' siblings plus the children.

To add siblings of the "main person" would be adding siblings to the parent - which can be seen in either case above by simply selecting the parent's parent.

To see more than one generation is what the Genealogy Report or the Outline Descendant Report is for. These type reports can show as many generations as you like.