using System.ComponentModel;

namespace SplittingViewsInMvvm.Models
{
    public class GuiModel : INotifyPropertyChanged
    {
        string _name;
        public string Name
        {
            get { return _name; }
            set
            {
                _name = value;
                raisePropertyChanged("Name");
            }
        }

        string _lastName;
        public string LastName
        {
            get { return _lastName; }
            set
            {
                _lastName = value;
                raisePropertyChanged("LastName");
            }
        }

        #region INotifyPropertyChanged Members
        public event PropertyChangedEventHandler PropertyChanged;
        void raisePropertyChanged(string propertyName)
        {
            var handler = PropertyChanged;
            if (handler == null) return;
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion
    }
}

using SplittingViewsInMvvm.Models;

namespace SplittingViewsInMvvm.ViewModels
{
    public class MainViewModel
    {
        public GuiModel GuiModelData { set; get; }

        public MainViewModel()
        {
            GuiModelData = new GuiModel();
            GuiModelData.Name = "Name";
            GuiModelData.LastName = "LastName";
        }
    }
}

<UserControl x:Class="SplittingViewsInMvvm.Views.Main"
             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" 
             mc:Ignorable="d" 
             xmlns:VM="clr-namespace:SplittingViewsInMvvm.ViewModels"
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
        <VM:MainViewModel x:Key="vmMainViewModel" />
    </UserControl.Resources>
    <StackPanel DataContext="{Binding Source={StaticResource vmMainViewModel}}">
        <GroupBox Margin="2" Header="Group 1">
            <TextBlock Text="{Binding GuiModelData.Name}" />
        </GroupBox>
        <GroupBox Margin="2" Header="Group 2">
            <TextBlock Text="{Binding GuiModelData.LastName}" />
        </GroupBox>
    </StackPanel>
</UserControl>

<UserControl x:Class="SplittingViewsInMvvm.Views.Group1"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <GroupBox Margin="2" Header="Group 1">
            <TextBlock Text="{Binding GuiModelData.Name}" />
        </GroupBox>
    </Grid>
</UserControl>

<UserControl x:Class="SplittingViewsInMvvm.Views.Group2"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <GroupBox Margin="2" Header="Group 2">
            <TextBlock Text="{Binding GuiModelData.LastName}" />
        </GroupBox>
    </Grid>
</UserControl>

<UserControl x:Class="SplittingViewsInMvvm.Views.Main"
             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" 
             mc:Ignorable="d" 
             xmlns:V="clr-namespace:SplittingViewsInMvvm.Views"
             xmlns:VM="clr-namespace:SplittingViewsInMvvm.ViewModels"
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
        <VM:MainViewModel x:Key="vmMainViewModel" />
    </UserControl.Resources>
    <StackPanel DataContext="{Binding Source={StaticResource vmMainViewModel}}">
        <V:Group1 />
        <V:Group2 />
    </StackPanel>
</UserControl>

<UserControl x:Class="SplittingViewsInMvvm.Views.Main"
             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" 
             mc:Ignorable="d" 
             xmlns:V="clr-namespace:SplittingViewsInMvvm.Views"
             xmlns:VM="clr-namespace:SplittingViewsInMvvm.ViewModels"
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
        <VM:MainViewModel x:Key="vmMainViewModel" />
    </UserControl.Resources>
    <StackPanel DataContext="{Binding Source={StaticResource vmMainViewModel}}">
        <V:Group1 DataContext="{Binding}" />
        <V:Group2 DataContext="{Binding}"/>
    </StackPanel>
</UserControl>