An InStr Issue

I am trying to find the first and last names of people in a cell. I have a userform to get their first and last names separately. I am trying to run a VBA macro to determine if each cell in a column contains both first and last names, and then put a "Y" in an adjacent column. The Code I have is as follows:

    Dim Last, i As Long
    Last = Cells(Rows.Count, "C").End(xlUp).Row
    MsgBox (Employee & " and " & Employee1)
    For i = Last To 1 Step -1
        If InStr(Cells(i, "C"), Employee) = 1 Then
            If InStr(Cells(i, "C"), Employee1) = 1 Then
                Cells(i, 6).Select
                If ActiveCell.Value = "Y" Then
                    Application.ScreenUpdating = True
                    Call Message1
                ElseIf ActiveCell.Value = "" Then
                    ActiveCell.Value = "Y"
                    Call Message3
                End If
            End If
        End If
Next

With just one InStr statement, it finds the first name just fine, but it isn't the right person, because there is more than one person with that first name. the second InStr won't allow it to find anything. I know I'm missing something simple, and would appreciate any help you can provide.