It may be worth pointing out that https://en.wikipedia.org/wiki/Selene
has not a single mention of Ambrogio or vampires. A look at https://en.wikipedia.org/wiki/Ambrogio
also does not contain any reference to vampires (or Selene). The list of Ambrogios, while containing a British robotic lawnmower, does not contain any person earlier than St Ambrogio https://en.wikipedia.org/wiki/Ambrose
who was born quite a lot later than the introduction of Selene into the Greek pantheon. I think the possible origin of this 'ancient legend' might be in a Harry Potter pastiche at fanfiction.net, but don't feel inclined to dig any deeper into the rehashings of this fairly certainly pseudo legend. There are definite references to the Ambrogio lawnmower and the saint easily found, but I have found nothing reliable for the 'vampire'. I may be missing something - feel free to prove me wrong.