About Joachim, as well as Nicolas and Aymeric, is the same of Amedeo;
About the three daughters, as well as their cousin Louise, I don't know, because it's a situation never happened before; the only one comparable to is the marriage of Astrid and Lorenz, but is however different, since Astrid was the daughter of the King and the second in the LoS; but according to the present law, nothing forbide but also nothing states that the husbands of the Princesses of Belgium have to be create Princes of Belgium.
Really, we only have to wait and see what will happen when one of King Albert and Queen Paola's granddaughters will marry.