Complex sentence: All in all, the Orleanist pretender then is postulated to be truly the Royal Blood for the Throne of France itself: the Carolingian line alive and well in France in the D'Orleans family, the rightful familial heir to the Throne of France.
Split into simpler sentences: All in all, the Orleanist pretender then is truly the Royal Blood for the Throne of France itself. The Carolingian line is alive and well in France in the D'Orleans family, the rightful familial heir to the Throne of France.