Main.xaml

<local:RequirementSelect Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="2" Margin="0 5 0 0" Value="{Binding Req, Mode=TwoWay}" />

RequirementSelect.xaml

<UserControl x:Class="HealthNav.Views.Controls.LetterTemplate.RequirementSelect"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:HealthNav.Views.Controls.LetterTemplate"
             mc:Ignorable="d" >
    <Grid>
        <StackPanel  Grid.Column="0" Grid.ColumnSpan="2" Orientation="Horizontal">
            <Label Margin="0 0 5 0">Voluntary:</Label>
            <CheckBox Name="ckbVoluntary" Margin="0 0 10 0" Checked="ckbRequirement_Checked" Unchecked="ckbRequirement_Checked" VerticalAlignment="Center" />
            <Label Margin="0 0 5 0">Mandatory:</Label>
            <CheckBox Name="ckbMandatory" Checked="ckbRequirement_Checked" Unchecked="ckbRequirement_Checked" VerticalAlignment="Center" />
        </StackPanel>
    </Grid>
</UserControl>

RequirementSelect.xaml.cs

using System;
using System.Windows;
using System.Windows.Controls;

namespace HealthNav.Views.Controls.LetterTemplate {
    /// <summary>
    /// Interaction logic for RequirementSelect.xaml
    /// </summary>
    public partial class RequirementSelect : UserControl {
        public RequirementSelect() {
            InitializeComponent();
        }


        public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
          "Value", typeof(Boolean), typeof(RequirementSelect), new PropertyMetadata(false));


        public string Value {
            get {
                return (string)this.GetValue(ValueProperty); ;
            }
            set {
                if (value.ToUpper().StartsWith("M")) {
                    ckbMandatory.IsChecked = true;
                    ckbVoluntary.IsChecked = false;
                } else if (value.ToUpper().StartsWith("V")) {
                    ckbMandatory.IsChecked = false;
                    ckbVoluntary.IsChecked = true;
                } else {
                    ckbMandatory.IsChecked = false;
                    ckbVoluntary.IsChecked = false;
                }

                this.SetValue(ValueProperty, value);
            }
        }

        private void ckbRequirement_Checked(object sender, RoutedEventArgs e) {
            

            CheckBox thisCheckbox = (CheckBox)sender;

            if (thisCheckbox.IsChecked == true) {
                CheckBox otherCheckbox = (thisCheckbox == ckbVoluntary ? ckbMandatory : ckbVoluntary);
                if (otherCheckbox.IsChecked == true) {
                    SetHooks(false);
                    otherCheckbox.IsChecked = false;
                    SetHooks(true);
                }
            }

            string val = "N";

            if (ckbVoluntary.IsChecked == true)
                val = "V";
            else if (ckbMandatory.IsChecked == true)
                val = "M";

            this.SetValue(ValueProperty, val);

            
        }

        private void SetHooks(bool Add) {
            if (Add) {
                ckbVoluntary.Checked += ckbRequirement_Checked;
                ckbVoluntary.Unchecked += ckbRequirement_Checked;
                ckbMandatory.Checked += ckbRequirement_Checked;
                ckbMandatory.Unchecked += ckbRequirement_Checked;
            } else {
                ckbVoluntary.Checked -= ckbRequirement_Checked;
                ckbVoluntary.Unchecked -= ckbRequirement_Checked;
                ckbMandatory.Checked -= ckbRequirement_Checked;
                ckbMandatory.Unchecked -= ckbRequirement_Checked;
            }

        }

    }
}