After a moment (and when Sy flies closer to see their faces), he'll realize that one of them is actually Diego's little sister, which kiiinda makes Essie his cousin too. (That blonde hair is VERY CONFUSING, okay.) Sy does not do apologies, but he'll begrudgingly tell the girls just to KEEP IT DOWN and fly off again to harangue his Keeper.
(Reid is the one who sparkles in the sunlight. Honestly, the vampire thing hasn't been disproven yet.)