回答編集履歴

  **ヘッダーのリサイズや入れ替えをさせない**のであれば、Grid等で偽のヘッダーをでっちあげます。

 

  できるだけ画像に寄せましたが、こんな感じでどうでしょうか？

  <Window

  x:Class="Questions306366.MainWindow"

  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:collections="clr-namespace:System.Collections;assembly=mscorlib"

  xmlns:sys="clr-namespace:System;assembly=mscorlib"

  Width="800"

  Height="450">

  <Window.Resources>

  <!-- 特に意味はない xamlのみ縛り -->

  <collections:ArrayList x:Key="data">

  <collections:ArrayList>

  <sys:Int32>1</sys:Int32>

  <sys:String>一郎</sys:String>

  <sys:DateTime>1998-01-01</sys:DateTime>

  <sys:Int32>22</sys:Int32>

  <sys:String>あ</sys:String>

  <sys:String>い</sys:String>

  <sys:String>う</sys:String>

  <sys:String>え</sys:String>

  </collections:ArrayList>

  <collections:ArrayList>

  <sys:Int32>2</sys:Int32>

  <sys:String>次郎</sys:String>

  <sys:DateTime>1999-02-02</sys:DateTime>

  <sys:Int32>21</sys:Int32>

  <sys:String>お</sys:String>

  <sys:String>か</sys:String>

  <sys:String>き</sys:String>

  <sys:String>く</sys:String>

  </collections:ArrayList>

  </collections:ArrayList>

 

  <Style TargetType="DataGridColumnHeader">

  <Setter Property="HorizontalContentAlignment" Value="Center" />

  </Style>

  <Style x:Key="CellStyleRight" TargetType="DataGridCell">

  <Setter Property="TextBlock.TextAlignment" Value="Right" />

  </Style>

  </Window.Resources>

 

  <Grid>

  <DockPanel>

  <!-- 偽ヘッダー -->

  <Grid

  Margin="1,1,1,0"

  Cursor="Arrow"

  DockPanel.Dock="Top"

  ForceCursor="True">

  <Grid.ColumnDefinitions>

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition Width="Auto" />

  <ColumnDefinition />

  </Grid.ColumnDefinitions>

  <Grid.RowDefinitions>

  <RowDefinition />

  <RowDefinition />

  <RowDefinition />

  </Grid.RowDefinitions>

  <DataGridColumnHeader Grid.RowSpan="3" Width="{Binding ActualWidth, ElementName=NumberColumn}" Content="番号" />

  <DataGridColumnHeader

  Grid.Row="1"

  Grid.RowSpan="2"

  Grid.Column="1"

  Width="{Binding ActualWidth, ElementName=NameColumn}"

  Content="名前" />

  <DataGridColumnHeader

  Grid.Row="1"

  Grid.RowSpan="2"

  Grid.Column="2"

  Width="{Binding ActualWidth, ElementName=DOBColumn}"

  Content="生年月日" />

  <DataGridColumnHeader

  Grid.Row="1"

  Grid.RowSpan="2"

  Grid.Column="3"

  Width="{Binding ActualWidth, ElementName=AgeColumn}"

  Content="年齢" />

  <DataGridColumnHeader

  Grid.Row="2"

  Grid.Column="4"

  Width="{Binding ActualWidth, ElementName=DDDDColumn}"

  Content="DDDD" />

  <DataGridColumnHeader

  Grid.Row="2"

  Grid.Column="5"

  Width="{Binding ActualWidth, ElementName=EEEEColumn}"

  Content="EEEE" />

  <DataGridColumnHeader

  Grid.Row="2"

  Grid.Column="6"

  Width="{Binding ActualWidth, ElementName=FFFFColumn}"

  Content="FFFF" />

  <DataGridColumnHeader

  Grid.Row="2"

  Grid.Column="7"

  Width="{Binding ActualWidth, ElementName=GGGGColumn}"

  Content="GGGG" />

 

  <DataGridColumnHeader Grid.Column="1" Grid.ColumnSpan="3" Content="個人情報" />

  <DataGridColumnHeader Grid.Column="4" Grid.ColumnSpan="4" Content="AAAA" />

  <DataGridColumnHeader

  Grid.Row="1"

  Grid.Column="4"

  Grid.ColumnSpan="2"

  Content="BBBB" />

  <DataGridColumnHeader

  Grid.Row="1"

  Grid.Column="6"

  Grid.ColumnSpan="2"

  Content="CCCC" />

  <Border />

  </Grid>

 

  <DataGrid AutoGenerateColumns="False" HeadersVisibility="None" ItemsSource="{StaticResource data}">

  <DataGrid.Columns>

  <DataGridTextColumn

  x:Name="NumberColumn"

  Width="90"

  Binding="{Binding [0]}"

  CellStyle="{StaticResource CellStyleRight}" />

  <DataGridTextColumn x:Name="NameColumn" Width="90" Binding="{Binding [1]}" />

  <DataGridTextColumn

  x:Name="DOBColumn"

  Width="90"

  Binding="{Binding [2], StringFormat=M月d日}"

  CellStyle="{StaticResource CellStyleRight}" />

  <DataGridTextColumn

  x:Name="AgeColumn"

  Width="90"

  Binding="{Binding [3]}"

  CellStyle="{StaticResource CellStyleRight}" />

  <DataGridTextColumn x:Name="DDDDColumn" Width="90" Binding="{Binding [4]}" />

  <DataGridTextColumn x:Name="EEEEColumn" Width="90" Binding="{Binding [5]}" />

  <DataGridTextColumn x:Name="FFFFColumn" Width="90" Binding="{Binding [6]}" />

  <DataGridTextColumn x:Name="GGGGColumn" Width="90" Binding="{Binding [7]}" />

  </DataGrid.Columns>

  </DataGrid>

  </DockPanel>

  </Grid>

  </Window>

  ```

  

 

  ソート機能を生かすには`DataGridColumnHeader`の`Click`を拾い、ソースのソートをしてください。

 

  [DataGridColumnHeader.SortDirection プロパティ (System.Windows.Controls.Primitives) | Microsoft Docs](https://docs.microsoft.com/ja-jp/dotnet/api/system.windows.controls.primitives.datagridcolumnheader.sortdirection?view=net-5.0#System_Windows_Controls_Primitives_DataGridColumnHeader_SortDirection)

 

  [DataGridHeaderBorder.SortDirection プロパティ (Microsoft.Windows.Themes) | Microsoft Docs](https://docs.microsoft.com/ja-jp/dotnet/api/microsoft.windows.themes.datagridheaderborder.sortdirection?view=net-5.0#Microsoft_Windows_Themes_DataGridHeaderBorder_SortDirection)