In edit-mode only the current object is editable. If the eye is an own object edit-mode means your in editmode for this eye. If you want to change something else, you have to change to object-mode, select the object you want to change(head / body for example). Then you change back to editmode to edit the object ( head or body)
you have to click on the things you want to select(with right mouse button).
when box-selecting you'll have to drag the mouse after pressing b