Very hazy on this one, but I read it in English in I think the early 90s, although it may have been published in the 70s or even earlier. Probably YA.
General shape of the story is that the protagonist (I think a teenage boy, possibly with a friend or relative who was a girl of similar age) meet various members of a family, who turn out to be vampires (of the traditional/evil kind) and they have to defeat or escape them at the end. I think the first vampire met may have been a girl whom the protagonist found attractive.
Two more specific memories: I think there's a early scene where the protagonist notes someone has some vampiric traits and this is explained as being due to porphyria.
And a situation where (having noted beforehand the vampire legend of them having to count spilled rice etc.), one of the characters uses this to get away from an older vampire and it's implied it works (I think the girl vampire is heard saying that there's "something wrong with" the vampire who has got stuck counting).