Percy (like Percival). A knight of the round table. This name pops up a couple of times throughout the franchise as it was also Dumbledore's father's name (and one of his middle names) and as well as Percival Graves from the first Fantastic Beasts movie.
Ginevra is the Italian form of "Guinevere", King Arthur's wife.
Molly is a variant of "Mary" which is a name that's been used throughout the centuries, with the most recent being the Queen Consort in the early 20th century and Queen Elizabeth II's grandmother.
William, Charles, and George are also ubiquitous names throughout history but all have current Royal bearers. (Although Prince George was born after the original series ended).
Frederick was an 18th century British King.
Merope (Gaunt) was known as the lost Pleiade (minor deities), as unlike her sisters - who all paired up with gods - she fell in love with a mortal and so died a mortal death.
Sirius and Regulus Black are both named after stars; their relative Andromeda is named after a galaxy, although almost the entire Black family (including off-shoots like the Malfoys) follow Stellar Theme Naming.
Fenrir is a Norse mythological wolf and Fenrir Grayback is a werewolf.
There are twins of Indian descent named Parvati (Hindu goddess of fertility, love, beauty, harmony, marriage, children, and devotion) and Padma ( Hindu goddess of prosperity, good luck, and beauty) Patil.
Draco Malfoy's grandfather was named Abraxas which is a Greek mythological world, connected with the number 365 and part of the solar cycle.
Madame Rosmerta's name was inspired by Greco-Roman mythology.
Gellert Grindelwald's second name may have been inspired by Beowulf but is also a town in Switzerland.