Why are you inserting activex controls? Surely simply inserting the images in-line as links would suffice? If you wish to constrain the sizes, put them in table cells of fixed width or frames.

If you are creating the charts in Excel, you could simply link to the charts themselves.

You can update the links with the following macro

Sub UpdateAllFields()
Dim oStory As Range
    For Each oStory In ActiveDocument.StoryRanges
        oStory.Fields.Update
        If oStory.StoryType <> wdMainTextStory Then
            While Not (oStory.NextStoryRange Is Nothing)
                Set oStory = oStory.NextStoryRange
                oStory.Fields.Update
            Wend
        End If
    Next oStory
lbl_Exit:
    Set oStory = Nothing
    Exit Sub
End Sub