MVVM How do I share a property between 2 views

Question

What i would like to achieve is when user changes a weekrange on View1, id like the dropdown value on View2 to update as well. As it stands, One does not update the other.

My setup

Bootstrapper.cs

Using prism, I've created a singleton type that I would need to share between 2 views.

class Bootstrapper : UnityBootstrapper
{
    protected override void ConfigureContainer()
    {
        base.ConfigureContainer();
        ...
        Container.RegisterType<IRTGSingletonService, RTGSingletonService>(new ContainerControlledLifetimeManager());
        ...
    }
}

IRTGSingletonService.cs / RTGSingletonService.cs

This object has 2 Enums SortBy and Weekrange and 2 EnumDataSource. lets focus on Weekrange

public interface IRTGSingletonService
{
    WeekRanges WeekRange { get; set; }
    EnumDataSource WeekRangeDataSource { get; set; }
}

public class RTGSingletonService : BindableBase, IRTGSingletonService
{
    private readonly IEventAggregator _ea;
    private readonly IRepository _repository;

    private WeekRanges _weekRanges;

    public RTGSingletonService(IEventAggregator ea, IRepository repo)
    {
        _ea = ea;
        _repository = repo;

        WeekRange = WeekRanges.LastMonth;
    }

    #region Week Range

    public EnumDataSource WeekRangeDataSource { get; set; } = new EnumDataSource { EnumType = typeof(WeekRanges) };

    public WeekRanges WeekRange
    {
        get => _weekRanges;
        set => SetProperty(ref _weekRanges, value, OnWeekRangeChanged);
    }

    private void OnWeekRangeChanged()
    {
        // TODO
    }

    #endregion
}

WeekRangesControl.xaml

To prevent repeating myself, Ive created a reusable control.

<UserControl x:Class="AdImpactAnalysis.Controls.WeekRangesControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
             mc:Ignorable="d">           

    <Grid x:Name="LayoutRoot">
        <telerik:RadComboBox ToolTip="Select a date range."
                             ItemsSource="{Binding DataSource}"
                             SelectedIndex="{Binding SelectedItem, Mode=TwoWay, Converter={StaticResource EnumConverter}}"
                             SelectedValuePath="Name" />
    </Grid>
</UserControl>

WeekRangesControl.cs

public partial class WeekRangesControl : UserControl
{
    /// <summary> Identified the DataSource dependency property </summary>
    public static readonly DependencyProperty DataSourceProperty = DependencyProperty.Register(nameof(DataSource), typeof(EnumDataSource), typeof(WeekRangesControl));

    /// <summary> Identified the SelectedItem dependency property </summary>
    public static readonly DependencyProperty SelectedItemProperty = DependencyProperty.Register(nameof(SelectedItem), typeof(WeekRanges), typeof(WeekRangesControl));

    /// <summary> Gets or sets the DataSource. </summary>
    public EnumDataSource DataSource
    {
        get => (EnumDataSource)GetValue(DataSourceProperty);
        set => SetValue(DataSourceProperty, value);
    }

    /// <summary> Gets or sets the SelectedItem. </summary>
    public WeekRanges SelectedItem
    {
        get => (WeekRanges)GetValue(SelectedItemProperty);
        set => SetValue(SelectedItemProperty, value);
    }

    public WeekRangesControl()
    {
        InitializeComponent();
        LayoutRoot.DataContext = this;
    }
}

View1.xaml / View2.xaml

These 2 views are tabs, only one view can be visible to the user at a time. (Kinda hoping this wont be an issue...)

This control is added to my 2 views like below

    <StackPanel Grid.Column="0">
        <controls:WeekRangesControl DataSource="{Binding SingletonService.WeekRangeDataSource}"
                                    SelectedItem="{Binding SingletonService.WeekRange, Mode=TwoWay, Converter={StaticResource EnumConverter}}" />

    </StackPanel>

View1ViewModel.cs / View2ViewModel.cs

    public View1ViewModel(IEventAggregator ea, IRepository repo, IRTGGroupsService gm, IRTGPredictionsService<RTG_Lookup2_Group> pm, IRTGSingletonService ss)
    {
        ...
    }


    public View2ViewModel(IEventAggregator ea, IRepository repo, IRTGGroupsService gm, IRTGPredictionsService<RTG_Lookup2_Group> pm, IRTGSingletonService ss) 
    {
        ...
    }

The issue I am having is when i select a weekrange on View1, View2 shows a different selected value.

Something i noticed and worth mentioning is, from here, the first time View2 is changed, my weekrange setter does not fire until i select a weekrange a second time. But even then, View1 will not update with the value from View2.

Any help would be appreciated. thanks