How to "connect" objects in 2 classes to make them update each other?

I have complicated problem (maybe with simple answer).

I have class, that contains some lines, points and "Markers".

Marker is a class that contains Ellipse and its center coordinates (Point).

Marker class has drag-drop implementation, that moves ellipse and changes Marker.coordinates property. That works.

However I want to use drag-drop from my Marker class to move points in SomeShape object (Marker objects are parts of SomeShape).

I thought, that when I create Marker object and I pass 'SomeShape.lineEnds[0]' to Marker constructor - update on Marker class will update also my SomeShape.lineEnds[0], but Its not working.

How can I solve this? By using some references somehow?

I hope I described my problem clearly enough.

Code:

class SomeShape
{
    // this object is set of lines and "Markers" (class below)

    private List<Marker> markers;
    private List<Point> lineEnds;
    private List<Line> lines;

    // my object can redraw itself on canvas
    public RedrawMe()
    {
        // it removes own lines from canvas and it puts new lines 
        // I call this function after I add points to lineEnds collection etc.
        // or when I change coordinates on one of lineEnds (list of points)

    }

    public void AddPoint(Point p)
    {
        this.lineEnds.Add(p); // adding point to line ends
        this.markers.Add(new Marker(p, this, c)); // adding same point to new marker

        RedrawMe();
    }

}

Problematic part:

class Marker
{
    public Canvas canvas;

    private Ellipse e;
    private Point coordinates; // ellipse center coordinates
    private Object parent; // I store SomeShape object here to call RedrawMe method on it


    public Marker(Point p, Object par, Canvas c)
    {
        this.coordinates = p;
        this.canvas = c;
        this.parent = par;

        e = MyClassFactory.EllipseForMarker();

        e.MouseDown += new System.Windows.Input.MouseButtonEventHandler(e_MouseDown);
        e.MouseMove += new System.Windows.Input.MouseEventHandler(e_MouseMove);
        e.MouseUp += new System.Windows.Input.MouseButtonEventHandler(e_MouseUp);

        c.Children.Add(e);

        e.Margin = new Thickness(p.X - (e.Width/2), p.Y -  (e.Height/2), 0, 0);
    }

    public void MoveIt(Point nc) // nc - new coordinates
    {
        this.e.Margin = new Thickness(nc.X - (e.Width / 2), nc.Y - (e.Height / 2), 0, 0);
        this.coordinates.X = nc.X;
        this.coordinates.Y = nc.Y;

        if (this.parent is SomeShape) ((SomeShape)parent).RedrawMe();
    }

    #region DragDrop  // just drag drop implementation, skip this


            private bool is_dragged = false;

        void e_MouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e){
            e.Handled = true;
            is_dragged = false;
            this.e.ReleaseMouseCapture();
        }
        void e_MouseMove(object sender, System.Windows.Input.MouseEventArgs e) {
            if (is_dragged)
            {
                this.MoveIt(e.GetPosition(canvas));
            }
        }
        void e_MouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e) {
            is_dragged = true;
            this.e.CaptureMouse();
        }

    #endregion // DragDrop
}