Graph non-adjacent column data

I'm trying to generate a line graph using VBA that selects data from alternating columns. I've included a spreadsheet that contains data for staff allocation (Forecast and Actual) over time.

I'd like to be able to create a graph that plots just the forecast columns for the following rows:
"Total Staff"
"Total Allocation"
"Remaining availability"

Alternatively, I'd like to create a graph that plots a comparison of Forecast vs Actual rows:
"Total Staff"
"Total Allocation" and
"Remaining availability".

I'm having difficulties with understanding how to set the correct range.

I'm using the following code but it's throwing an error:

Sub linegraph()
'
' linegraph Macro

'

 Dim AltRng As Range
  Dim LastCol As Variant
  Dim Rng As Range
  Dim RngEnd As Range
  Dim Wks As Worksheet
  
   Set Wks = ActiveSheet
    LastCol = Wks.Cells.Find("*", , xlValues, xlWhole, xlByColumns, xlPrevious, False).Column

    'column 5 starting point for forecast data

      For C = 5 To LastCol Step 2
        Set Rng = Wks.Columns(C)
          If AltRng Is Nothing Then Set AltRng = Rng
          Set AltRng = Union(AltRng, Rng)
      Next C
      
  
   With ActiveSheet.ChartObjects.Add _
            (Left:=100, Width:=375, Top:=75, Height:=225)
         .Chart.SetSourceData Source:=Sheets("Sheet1").Range(AltRng)
        .Chart.ChartType = xlXYScatterLines
    End With


End Sub

thank you for your help