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