Exclude certain cells

I have tried to find a solution to exclude certain cells in a range all over the place but I still haven't found what I am looking for. Maybe someone here can help me?

The point is to exclude C20:C21, C33:C34 etc from the fillrange below (C9:C122) and I guess there is a very simple solution for the problem?

Worksheets("MB_Vol").Range("C9").FormulaR1C1 = "=AVERAGE(RC[8]:RC[9])"
Set SourceRange = Worksheets("MB_Vol").Range("C9")
Set fillRange = Worksheets("MB_Vol").Range("C9:C122")
SourceRange.AutoFill Destination:=fillRange, Type:=xlFillValues

Another problem I have is how to include several sheets into this?

Set SourceRange = Worksheets("MB_Vol").Range("C9")
Set fillRange = Worksheets("MB_Vol").Range("C9:C122")

I want to write it like this, but this isn't working:

Set SourceRange = Worksheets("MB_Vol", "MB2_Vol", "MB3_Vol").Range("C9")
Set fillRange = Worksheets("MB_Vol", "MB2_Vol", "MB3_Vol").Range("C9:C122")

Any ideas?

Thanks in advance!