I think the best solution in the case of a menu is to join the two images in one. Consider making a pdf.
There is a solution that may not be as elegant, but as I already solved a similar problem so I will post, and if someone put a more "elegant" answer consider it.
You can put another download to be done together with Javascript.
function dowload(){
document.getElementById('btn_imagem2').click();
}
<a class="btn btn-primary" href="images/cant3.png" download="cant3.png" onclick="dowload()">Baixe nosso Cardápio Físico</a>
<!--Aqui é a segunda imagem que pretende fazer o dowload-->
<a id="btn_imagem2" class="btn btn-primary" href="images/cant4.png" download="cant4.png" hidden="true">Baixe nosso Cardápio Físico</a>
So when the user clicks on button 1, you force him to click button 2, which he is not even seeing (notice the property Hidden="true").
this will make the two download event be fired.