Hagena: a king of the Rugians, famous from the Hild Saga, also the foe of Heoden below
Holmrygas: All editions note that the 'g' is missing from the manuscript and they add it back in. Malone, in his glossary, makes the additional correction of a 'c', rendering this holmrycgas, holmrycgum. Malone identifies the Rugians as the Hulmerugi of Jordanes, in the islands of the estuary of the Vistula. (174)
Heoden: The ASPR XML has this word tagged as 'unclear' and it truly is. The OEPIF project shows it as very unclear as well. Malone reads it as Henden but says it is the character Heoden of the Hild saga (pg 168). Chambers and ASPR both record it as 'Heoden', so that is what I'm going to stick with for now.