first name - paternal surname - maternal surname
the paternal surname is the surname that usually gets adopted
so when you guys are doing the whole Maria Clara Carriedo de la Cruz stuff or whatever, you've been taking the wrong surname from Spain's character all along!
His name is Antonio Fernandez Carriedo
Antonio = first name
Fernandez = paternal surname
Carriedo = maternal surname
so the surname that would be more accurate to borrow would be Fernandez, not Carriedo!
BUT BUT BUT BUT BUT
Why borrow Spain's surnames in the first place? You don't see America being called Alfred Kirkland. You don't see Lovino Fernandez. If your character is an independent nation, I don't see any reason for them to keep their coloniser's surname as though they're still their colony.
I get it if you headcanoned the OC as having the surname during colonisation. But once they are independent, it would make sense for them to break away from that. Perfect sense in fact. They're independent and that human name still having their coloniser's surname makes it feel like they're still their coloniser's 'property', so to speak.
So basically what many people have done is
1. borrow the incorrect surname from Spain
2. made their PH OC seem less independent and still Spain's property even though Philippines has gone through two other colonisers (America, Japan) and is now independent
JUST STOP WITH THE GODDAMN 'CARRIEDO' OKAY THAT'S INACCURATE