Specific sub to open a workbook (hidden) so multiple subs can access the worksheets

asmenut , 
If I understand your need, I would create a function to get the workbook for each routine. The function would only open the workbook if it isn't already open.  So if a subroutine needs the workbook it would call GetWkb(). GetWkb() would see if the workbook is open, and if so, return it (quick!). If it isn't open, it would open it and return it. 

Here is an example of one of the calling routines

Sub Sub1()
    Dim oWkb As Workbook
    Set oWkb = GetWkb
    'Do something with the workbook here
End Sub

The function would be:

Public Function GetWkb() As Workbook

    Static oWkb As Workbook              'Static to keep it in memory when this function ends
    Const sWkb As String = "MyData.xlsx" 'Change this to your master workbook's name
    Const sPath As String = "C:\Temp\"   'Change this to your master workbook's path

    On Error GoTo ErrHandler

    If Not oWkb Is Nothing Then
    '    Make sure it hasn't been closed by some other process
        If oWkb.Name = vbNullString Then Set oWkb = Nothing
    End If

    If oWkb Is Nothing Then
    '   See if it was opened by some other process
        Set oWkb = Application.Workbooks(sWkb)
    '   If still nothing, open the workbook 
        If oWkb Is Nothing Then
            Set oWkb = Application.Workbooks.Open(Filename:=sPath & sWkb, ReadOnly:=True)
            ActiveWindow.Visible = False
        End If
    End If
    Set GetWkb = oWkb

ErrHandler:
    Select Case Err.Number
        Case Is = 0:                       'No Error, Do nothing
        Case Is = 9: Resume Next           'Workbook not open error
        Case Is = -2147221080: Resume Next 'Workbook closed error
        Case Else:
        '   Some unanticipated error happened so report it
            MsgBox _
              Prompt:="Error#" & Err.Number & vbLf & Err.Description, _
              Buttons:=vbCritical + vbMsgBoxHelpButton, _
              Title:="GetWkb", _
              HelpFile:=Err.HelpFile, _
              Context:=Err.HelpContext
    End Select

End Function

Hope that helps