if they're all in a separate column, maybe this will help. i used sheet1 and
column B in my example.

Sub test()
     Dim ws As Worksheet
     Dim lastrow As Long
     Dim rng As Range
     Dim cell As Range
     Dim cntr As Long
     Set ws = Worksheets("Sheet1")
     lastrow = ws.Cells(Rows.Count, "B").End(xlUp).Row
     Set rng = ws.Range("b2:B" & lastrow)

     For Each cell In rng
           If Len(cell) > 1 Then
                 cell.Interior.ColorIndex = 19
                 cntr = cntr + 1
           Else
           cell.Interior.ColorIndex = 0
           End If
     Next
MsgBox cntr & " names with more than 1 character."
End Sub

You can use Conditional Formatting.  Highlight the range of cells
containing the middle names.  Choose Tools|Conditional Formatting.
Select "Formula Is" from the drop down box and place this formula in
the textbox (assuming column D contains the middle names).
=LEN(D2)>1

Then click the Format button and change the formatting that will be
displayed if the length is greater than 1.