Ok, consertou tudo. :)
E respondendo a minha própria pergunta, lol - Apenas pelo amor do googles.
Private Sub Workbook_Open()
Const fromFile = "NetworkDriver\Folder\Workbook.xlsx"
Application.DisplayAlerts = False
Sheets("Sheet8").Delete
Sheets("Sheet9").Delete
Application.DisplayAlerts = True
Dim srcBook As Workbook
Dim wkb As Workbook
Set wkb = ActiveWorkbook
' open workbook and set reference!
Set srcBook = Application.Workbooks.Open(fromFile, _
UpdateLinks:=False, _
ReadOnly:=True, _
AddToMRU:=False)
Application.ScreenUpdating = False
srcBook.Sheets("Sheet8").Copy After:=ThisWorkbook.Sheets(ThisWorkbook.Sheets.Count)
srcBook.Sheets("Sheet9").Copy After:=ThisWorkbook.Sheets(ThisWorkbook.Sheets.Count)
srcBook.Close False
wkb.Sheets("Sheet8").Visible = False
wkb.Sheets("Sheet9").Visible = False
Application.ScreenUpdating = True
End Sub