> Sigmundur kom austan og þeir félagar.
> Sigmund came from the east and those companions.

"S. and his companions came from the east." "S. came west with his
companions." In Old Norse a plural subject after a conjunction can
include a singular subject before the conjunction like this. There's
another example quoted in the Old Norse Online course:

konungr var allmjök drukkinn ok bæði þau
"the king was quite drunk, as was she"

(more literally: the king was quite drunk and both of them [were])

http://www.utexas.edu/cola/centers/lrc/eieol/norol-6-X.html#Nor06_GP28

> Vér höfum illt verk unnið
> We have bestowed?

"We have done an evil deed." 'unnið' (=unnit) is the neuter past
participle of 'vinna' "to do, perform, accomplish, etc." The
neut.p.p. of 'unna' "to grant, bestow, not grudge, etc." would be
'unnað' (=unnat) or 'unnt' (both forms occur).

LN