The "vampire attack events" you are referring to are usually called "community lot break-ins". This is a bug that has been happening since the vampire pack released. They tried to fix it once, but it didn't really work. So it continues.
There is no danger involved as these vampires can't do anything to anyone on a community lot (not even to normal sims). The only thing it does is lock up your game while the "event" is taking place. In any case, vampires cannot drink from other vampires.
You can try using options from the "friendly" menu to make them leave but results will vary. If sparring works, then yes, use it. Otherwise, you just have to wait until the vampire leaves on their own which ends the event.
