The thing with IGA Idk about, but it makes little difference in a fictional story. Mathias Cronqvist was taken off Mathias Corvinus who had a wife named Elisabetha, it's a different universe to our own.
X, that's my point though, having a mystical bloodline wouldn't classify as a 'curse' as such.
Curse:
a solemn utterance intended to invoke a supernatural power to inflict harm or punishment on someone or something
If anything the curse begins after LOI when Sara is sacrificed to complete the very weapon which the Belmonts require to 'hunt the night'.
By the same token you could argue Mathias/ Drac is cursed to be forever hunted by the Belmonts.
Unless a future entry to the og canon argues, mystical bloodline or not we can't be sure what happened to the Belmonts before LOI.