Adjust Buttons to the widthest one

How can I do to make the buttons width adjust to the widthest one.

https://goo.gl/photos/u2QdBJPGydmGY5QLA

VerticalLayout midLeft = new VerticalLayout(btnAsignar, btnCombinar, btnReemplazar, btnCancelar);
midLeft.setSpacing(true);

If I setSizeFull() to some of them , they readjust to the biggest one, but if I set all them with SizeFull, the setting get lost

btn1.setSizeFull();
btn2.setSizeFull();
//btn3.setSizeFull(); //this is the one with a largest caption (for now)
btn4.setSizeFull();

must be a better way to achieve this