main workbook : Including this macro

WB1 and WB1A-actual schedule : ?

WB2=Sched + Pickups Week 1 : this week

WB3=Sched + Pickups : the next weeks

I'm not quite sure what you want to do, but do you want to open WB2 or WB3 in the main workbook's macro?

What if strgen is passed the number of weeks as an argument?

Function strgen(weeks As Long)
    ' weeks 1 : this weekend(Sunday) Sunday-Saturday next Sunday
    '       2 : next weekend(Sunday)
    strgen = Format(Date - Weekday(Now(), 1) + 1 + (weeks * 7), "mm.dd.yy") & ".xlsm"
End Function

How about doing it as follows in the macro you run?

Sub test()
    Dim strDirPath As String
    Dim strFilename1 As String
    Dim strPath1 As String
    Dim strFilename2 As String
    Dim strPath2 As String
    Dim strFilename As String
    Dim strPath As String
    Dim result As VbMsgBoxResult
    
    strDirPath = "C:\Temp\Orginal Schedules\"
    strFilename1 = "SCHED " & strgen(1)
    strPath1 = strDirPath & strFilename1
    strFilename2 = "SCHED " & strgen(2)
    strPath2 = strDirPath & strFilename2
    If Dir(strPath1) <> "" Then
        If Dir(strPath2) <> "" Then
            Select Case Weekday(Now(), 1)
                Case 1 To 3
                    strFilename = strFilename1
                Case 4
                    result = MsgBox("It is Wednesday. Do you want to open """ & strFilename1 & """", vbYesNo + vbQuestion, "Confirmation")
                    If result = vbYes Then
                        strFilename = strFilename1
                    Else
                        strFilename = strFilename2
                    End If
                Case Else
                    strFilename = strFilename2
            End Select
        Else
            strFilename = strFilename1
        End If
    ElseIf Dir(strPath1) <> "" Then
        strFilename = strFilename2
    Else
        MsgBox "file does not exist.", vbOKOnly + vbCritical
        Exit Sub
    End If
    strPath = strDirPath & strFilename

    Workbooks.Open Filename:=strPath
    Windows(strFilename).Activate
End Sub