Using checkboxes in a grouped vb.net datagrid

I have three kind of separate checkbox questions, all related to their use in the same datagrid.

1. I've loaded a datatable, dtAll, into a datagrid, dgdList, and bound each column to the imported data. The datagrid also has an initial column with checkboxes. How can I determine which rows of data have been checked. The intended functionality is for a user to mark two duplicates and merge together. I need to be able to gather row data from the datatable or datagrid whenever the checkbox column is checked

2. When I group my datagrid into tables, below, it somehow turns off my ability to check more than one checkbox. Everytime i select a new row, it clears all previous checkboxes. I would like to be able to check boxes in multiple rows. (Further, I have to click twice, once to select the row, once to edit the value of the checkbox to true - it would be great if I could do it in a single click).

   <!-- language: lang-vb -->

    Dim myView As System.ComponentModel.ICollectionView
    myView = CollectionViewSource.GetDefaultView(dtAll)
    myView.GroupDescriptions.Add(New PropertyGroupDescription("GROUP ID"))
    dgdList.ItemsSource = dtAll.DefaultView
   

3. I've added a checkbox to the group header. When clicked, I'd like it to fill in each checkbox in all the rows inside of that group. Is there any way I can do this as well? If it helps, below is the Xaml code I'm using to split up groups of records

   <!-- language: lang-xml -->

     <DataGrid.GroupStyle>
        <GroupStyle>
            <GroupStyle.HeaderTemplate>
                <DataTemplate>
                    <StackPanel>
                        <TextBlock Text="{Binding Path=Name}" />
                    </StackPanel>
                </DataTemplate>
            </GroupStyle.HeaderTemplate>
            <GroupStyle.ContainerStyle>
                <Style TargetType="{x:Type GroupItem}" x:Name="Style1">
                    <Setter Property="Template" x:Name="Setter1">
                        <Setter.Value>
                            <ControlTemplate TargetType="{x:Type GroupItem}" x:Name="ControlTemplate1">
                                <Expander IsExpanded="True" Name="Expander1">
                                    <Expander.Header>
                                        <StackPanel Orientation="Horizontal">
                                            <CheckBox Name="CheckBox9" />
                                            <TextBlock Text=" Exact Name Match Group #"/>
                                            <TextBlock Text="{Binding Path=Name}" />           
                                        </StackPanel>
                                    </Expander.Header>
                                    <ItemsPresenter />
                                </Expander>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </GroupStyle.ContainerStyle>
        </GroupStyle>
    </DataGrid.GroupStyle>