invisibleTwin = new Button("Twin");
invisibleTwin.setId("twin");
invisibleTwin.setVisible(false);
twinPane.getChildren().setAll(invisibleTwin, visibleTwin);
window = new Stage();
window.setTitle("window");
window.setScene(new Scene(pane, 600, 400));
otherWindow = new Stage();
otherWindow.setTitle("otherWindow");
otherWindow.setScene(new Scene(otherPane, 600, 400));
twinWindow = new Stage();
twinWindow.setTitle("twinWindow");
twinWindow.setScene(new Scene(twinPane, 600, 400));
window.show();
otherWindow.show();
twinWindow.show();