Edit existing VBA to remove duplicates and include conditional?

I'm new to VBA and would appreciate help modifying this code. I'm using the code below in the workbook attached. It removes duplicates in Sheet1 and copies values located in Sheet1B&C into Sheet2A&B. The problem is when it copies the data over it creates a ton of duplicates in Sheet2. I need to modify the code to only copy over data from Sheet1B&C to Sheet2A&B if it's not already located in Sheet2 e.g. if the data in Sheet1B3&C3 are already located in Sheet2A&B as a pair in the same row it DOESN'T need to be copied over. I need to eliminate duplicate values in A&B of Sheet2; only unique values should remain.

I need the data I'm copying from Sheet1 to be copied over as pairs of data in the same row e.g. A2&B2, A3&B3. If duplicates ever appear in Sheet2 they need to be deleted based on whether or not there's data in D and/or C of the same row. If there's data in C and/or D I need the duplicate without data in C and/or D to be deleted.

I then need to include a conditional format that highlights and row A:D in Sheet2 if C and/or D is blank.

Sub Macro1()
Dim sh1 As Worksheet, sh2 As Worksheet, lr As Long, rng As Range, c As Range, loc As Range
Set sh1 = Sheet1
Set sh2 = Sheet2
lr = sh1.Cells(Rows.Count, 1).End(xlUp).Row
sh1.Range("A2:D" & lr).Sort Range("A1"), xlAscending, Range("B1"), , , Range("C3"), xlAscending, Header:=xlNo
    For i = lr To 3 Step -1
        With sh1
            If .Cells(i, 1) = .Cells(i - 1, 1) And .Cells(i, 2) = .Cells(i - 1, 2) _
                And .Cells(i, 3) = .Cells(i * 1, 3) Then
                    If .Cells(i, 4).Value > .Cells(i - 1, 4).Value Then
                        .Cells(i - 1, 4).EntireRow.Delete
                    Else
                        .Cells(i, 4).EntireRow.Delete
                    End If
            End If
        End With
    Next
Set rng = Intersect(sh1.Range("B2").Resize(Rows.Count - 2, 1), sh1.UsedRange)
    For Each c In rng
        Set loc = sh2.Range("A2", sh2.Cells(Rows.Count).End(xlUp)).Find(c.Value)
            If Not loc Is Nothing Then
                If loc.Offset(0, 1) <> c.Offset(0, 1) Then
                    c.Resize(1, 2).Copy sh2.Cells(Rows.Count, 1).End(xlUp)(2)
                End If
            Else
                c.Resize(1, 2).Copy sh2.Cells(Rows.Count, 1).End(xlUp)(2)
            End If
            
    Next
End Sub

0SAMPLE.xlsm