Heðca: Malone corrects this to Hehca, and associates him with 'Hache', a Germanic hero (Malone 168). Anscombe 1916 amends it to Hæþcan and identifies the character with King Hæðcyn of Beowulf.
Beadeca: Malone speculates that this may be the Baduila (later called Totila) of history Wikipedia (Malone 130).
Herelingas: The followers of Herela, or King Herla of medieval writer Walter Map (Wikipedia), the leader of the Wild Host (or Woden in disguise), but the poet here is likely referring to the Harlun brothers (Malone 170).