Considering that Vlad the Impaler lived in the 15th century, that gives roughly 550 years of time for Vlad's descendants to be "fruitful and multiply". Let's say he has two kids. In twenty years, those two kids have two kids. Let's start the clock at 1460. In generation 1, Vlad has two descendants. By 1480 he has four. By 1500 he has eight. Robert Pattinson was born in 1986. So that's roughly twenty-six generations between Vlad and Pattinson. So if this very rough model is correct, there are about 67,108,864 descendants of Vlad living today. I'm not impressed.
But then again, my model also states that Charlemagne today has 4.61168602 × 10^18 living descendants. That's well... at lot more people living today on Earth.