Move object when mouse move on helix- viewport 3D?

i try to move multiple object open on Helix viewport 3D. so curtly mutiple object are open succesfuly. but problem in when i try to move any specific model at that time object move mouse opposit position like when i move on Right side at time object is goes to left side same as all axis. so i past here mouse move click event hrer, please provide a solution.

Number of query -

multiple object open at time i need to select particular object and move it. curntly all model are move in oposite axix.

Mouse move time object move opposite direction.

Object load Event :

private void loadbtn_Click(object sender, RoutedEventArgs e)
{
            Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();

            dlg.DefaultExt = ".stl";
            dlg.Filter = "STL Files|*.stl;";
            Nullable<bool> result = dlg.ShowDialog();
            if (result == true)
            {
                string filename = dlg.FileName;
                openfile = filename;
               // txt1.Text = dlg.FileName;
            }
            ModelVisual3D device3D = new ModelVisual3D();
            device3D.Content = Display3d(openfile);
            // viewPort3d.Children.Add(device3D);

            var reader = new StLReader();
            _modelGroup = reader.Read(openfile);
   
            var modelVisual = new ModelVisual3D();
            modelVisual.Content = _modelGroup;

            // Apply the TranslateTransform3D to your STL object
            _modelGroup.Transform = _translate;

            // Add the ModelVisual3D to the Children property of the HelixViewport3D
            viewPort3d.Children.Add(modelVisual); 
}

Mouse Down event is as per below.

private void viewPort3d_MouseDown(object sender, MouseButtonEventArgs e)
      {
         //*** MOVE ***
          var position = e.GetPosition(viewPort3d);
          var origin = new Point3D(position.X, position.Y, 0);
          Point originPoint = new Point(origin.X, origin.Y);
          var transformedOrigin = Viewport3DHelper.UnProject(ConvertToViewport3D(viewPort3d),           originPoint);
          _lastPosition = position;
          viewPort3d.MouseMove += viewPort3d_MouseMove;
          viewPort3d.MouseUp += viewPort3d_MouseUp;
      }

private Viewport3D ConvertToViewport3D(HelixViewport3D helixViewport)
        {
            Viewport3D viewport = new Viewport3D();
            viewport.Camera = helixViewport.Camera;
            foreach (var child in helixViewport.Children)
            {
                if (child is ModelVisual3D modelVisual)
                {
                    if (modelVisual.Content is Model3D model)
                    {
                        ModelVisual3D newChild = new ModelVisual3D();
                        newChild.Content = model;
                        viewport.Children.Add(newChild);
                    }
                    else
                    {
                        // handle other types of modelVisual.Content if necessary
                    }
                }
                else
                {
                    // handle other types of Visual3D objects if necessary
                }
            }
            return viewport;
        }

Mouse Move event is as per below.

private void viewPort3d_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
{
            System.Windows.Point position = e.GetPosition(this); // this = viewPort3D
            double pX = position.X;
            double pY = position.Y;

            _translate.OffsetX -=pX;
            _translate.OffsetY += pY;

            _lastPosition = position;
}

Mouse Up event is as per below.

private void viewPort3d_MouseUp(object sender, MouseButtonEventArgs e)
        {
            //_isDragging = false;
            viewPort3d.MouseMove -= viewPort3d_MouseMove;
            viewPort3d.MouseUp -= viewPort3d_MouseUp;
            //ReleaseMouseCapture();

        }