Binding Comboboxes inside an Itemscontrol - wpf

Question

I am having trouble with a combination of ComboBox'es inside an ItemsControl.
What I am trying to do is create a List of ComboBox'es. At the start there is only one default ComboBox with a default value. If you select any other type than the default type, a new ComboBox is added with the default type in it.
Now, each Item in the List actually contains of 2 Combobox'es. The second box displays the number, this type is present.
Before:
After:
Now I want to update the numbers in the second box if any other number in the ItemsControl changes. How do I do that?
Here is the relevant code:
<ItemsControl Grid.Column="0" Grid.Row="2" ItemsSource="{Binding ChosenAppartmentTypeList}" Margin="10">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<ComboBox Margin="10" SelectedIndex="0" ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:GeneralProjectDataView}}, Path=DataContext.AppartmentTypeList}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<i:InvokeCommandAction Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:GeneralProjectDataView}}, Path=DataContext.ComboBoxSelectedItemChangedCommand}" CommandParameter="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=ComboBox}, Path=SelectedItem}" />
</i:EventTrigger>
</i:Interaction.Triggers>
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
<ComboBox ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:GeneralProjectDataView}}, Path=DataContext.NumberList}" SelectedItem="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=ItemsControl}, Path=SelectedItem.Count}" SelectedIndex="0">
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Those are the lists:
public ObservableCollection<AppartmentType> AppartmentTypeList { get; set; }
public ObservableCollection<AppartmentType> ChosenAppartmentTypeList { get; set; }
And those are the properties:
public class AppartmentType : ValidatableBindableBase
{
private string name;
private int count;
public string Name
{
get { return name; }
set { SetProperty(ref name, value); }
}
public int Count
{
get { return count; }
set { SetProperty(ref count, value); }
}
}

Answer 1

First, you can observe your property ChosenAppartmentTypeList via PropertyChanged event and update the ApartmentType items.
Reference
Secondly, your SelectedItem on second combobox must be bound two-way.