But unless Philippe passes a new royal decree, their children will be HRH Prince/ss of Belgium.
He still needs Philippe's consent to marriage so their children can be HRH Prince/ss of Belgium.
It looks like the succession rights need consent to marriage, but the titles don't. Google translation of the 1991 decree:
Article 1. In public and private acts that concern, the Princes and Princesses from the immediate offspring of HRH Prince Albert, Félix Humbert Théodore Christian Eugène Marie, Prince de Liège, Prince of Belgium, will qualify Princes or Princesses of Belgium after their names.
Art. 2. The Royal Decree of 14 March 1891, calling Princes and Princesses of Belgium Princes and Princesses from the male and direct descendants of the late King Leopold I, is repealed.
So their children will be Princes/Princesses of Belgian. I honestly don't see the point in that decree. Amedeo will likely never have public duties representing Belgian and neither will his children. I would imagine the wedding will also probably take place in Italy - maybe a civil ceremony in Belgium, i dont know.
On one hand I don't see it being a big issue, on the other hand I can totally see Amedeo not asking. He is living a private life, I can recall seeing him once or twice a year and with Philippe having 4 children the succession is secured. I assume that Philippe and Laurent being childless for so long was the main reason behind the new decree. That's not an issue now and Astrid's children are "not needed" anymore. I may be wrong, but I predict that in the end Amedeo's and Lili's future children will be bearing just the Austria-Este titles.
I agree with both of you, Amedeo and his future children don't need
titles, but I agree with Dottie Caterpillar, too, both sides of his family love being royal (Daddy's family will fake it if they have to, Mommy's is one of the only RFs left in Europe whose "spares" get appanages and taxpayer paid mansions
). But the BRF is on shaky ground, so Philippe might rein it in.