How to have multi selection and checkbox work together in telerik WPF

I have check boxs inside my radchombobox and if I select multiple names it shows in the text field but noting happens till I click the check box then the radcombobox closes after one check. How to I combine both actions so if I select the names or check the check boxes it work. Also how do I get the combobox not to close after I check one item. New to telerik WPF thnka you

<Grid>
 <telerik:RadComboBox x:Name="radComboBox"
                             VerticalAlignment="Center"
                             Margin="0 50 0 0"
                             Grid.Column="1"
                             Grid.Row="1"
                             ItemsSource="{Binding Items}" 
                             AllowMultipleSelection="True">
                             
           <telerik:RadComboBox.ItemContainerStyle>
            <Style TargetType="{x:Type telerik:RadComboBox}">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate>
                            <StackPlanel Orientation "Horizontal">
                                <CheckBox IsChecked="{Binding Path=IsSelected, Mode=TwoWay}" 
                                          VerticalAlignment="Center"
                                          Width="5"/>
                                <TextBlock Text="{Binding Name}"/>
                            <StackPlanel>
                        <ControlTemplate>
                    <Setter.Value>
                <Setter>
            <Style>
                
           
           <telerik:RadComboBox.ItemContainerStyle>
           
        </telerik:RadComboBox>
<Grid>

"Name" is a string and "Items" is an ObservableCollection