Hello,

The nested content control is a RecordListControl, which holds the nested records. You would have to bind the XamDataCards directly to the DataItem. Here is the binding expression that you can use in the template of the ExpandableFieldRecordPresenter:

<igDP:XamDataCards DataSource="{Binding Path=Record.ParentDataRecord.DataItem.Relatives, RelativeSource{RelativeSource TemplatedParent}}"/>

There is another way to achieve this. You could use a CellValuePresenter style and custom positioning of the nested field. For example :

<igDP:Field Name="Relatives" IsExpandable="False" Row="1" Column="0" ColumnSpan="6">
   <igDP:Field.Settings>
      <igDP:FieldSettings CellValuePresenterStyle="{StaticResource RelativesStyle}"/>
   </igDP:Field.Settings>
</igDP:Field>

where the custom style is :

<Style TargetType="{x:Type igDP:CellValuePresenter}" x:Key="RelativesStyle">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="{x:Type igDP:CellValuePresenter}">
                                <igDP:XamDataCards DataSource="{Binding DataItem.Relatives}" x:Name="content"/>
                                <ControlTemplate.Triggers>
                                    <DataTrigger Binding="{Binding IsExpanded}" Value="False">
                                        <Setter Property="Visibility" Value="Collapsed" TargetName="content"/>
                                    </DataTrigger>
                                    <DataTrigger Binding="{Binding IsExpanded}" Value="True">
                                        <Setter Property="Visibility" Value="Visible" TargetName="content"/>
                                    </DataTrigger>
                                </ControlTemplate.Triggers>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>

 I have attached a sample demonstrating these two approaches.