public IQueryable GetAllPeople(string flag)
        {
            PeoplelEntities db = new PeopleEntities();

            var peopleAll = (from p in db.People

                             join t1 in db.Tabl1 on p.ID equals t1.ID

                             join t2 in db.Tabl2 on p.ID equals t2.ID into Temp2
                             from temp2 in Temp2.DefaultIfEmpty()

                             join t3 in db.Tabl3 on db.ID equals t3.ID into Temp3
                             from temp3 in Temp3.DefaultIfEmpty()
					
		  	и так далее ...................

                             where t1.Name == flag
                             orderby p.Name

                             select new { People = p.Name,Tabl2 = temp2.Name,Tabl3 = temp3.Name });        
            return peopleAll;    
        }

public MainWindow()
		{
			this.InitializeComponent();
			this.DataGrid_people.DataContext = new DAL.DataAccessLayer().GetAllPeople(flag);
		}

<DataGrid x:Name=" DataGrid _people" CanUserSortColumns="True" AutoGenerateColumns="False" ItemsSource="{Binding}" >
                <DataGridTextColumn Binding="{Binding People}"/>
                <DataGridTextColumn Binding="{Binding Tabl2}"/>
                <DataGridTextColumn Binding="{Binding Tabl3}"/>
</DataGrid>