Using checkboxes in a grouped vb.net datagrid

Question

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).

   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

    <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>