> þeir höfðingjar er svo voru vel að sér að heldur vildu frá hverfa en

brenna hann inni

chieftains who had the decency to turn aside rather than burn him in
his home

> því að þeir munu allt til vinna að yfir taki við oss

for they will do everything [they can] to get the better of us. See
Zoega `vinna' + preps.

> Munu þeir það ætla sem eigi er ólíklegt að það sé þeirra bani ef oss

dregur undan.

They will expect – as is not unlikely [i.e. and rightly so!] – that it
will be the death of them if we escape.

> Nú eru þeir feigir er þeir hafa inn gengið.

Now they're done for, having gone inside. (Rather than having a
temporal sense, `er' introduces a circumstamcial or explanatory clause
here: since, seeing as how they've gone inside. Their going inside is
the circumstance that explains why Flosi believes that their fate is
now sealed.)

> sem þykkvast

as tightly as possible. (Superlative of the adjective `þykkr' "think,
dense". He's telling them to close ranks as tightly as we can so that
no one can sneak out between them.)

> og bar að Hróaldi þegar allan skjöldinn

and drove the whole shield suddenly against Hróaldr

> hyrnan sú hin fremri

the upper point [of Skarpheðinn's axe].