> Þá tók Kjartan til orða og mælti til Bolla: "Hversu fús
> ertu frændi að taka við trú þeirri er konungur býður?"

> Then Kjartan began to speak and said to Bolla: "How
> willing are you, relative, to take their faith that the
> King proclaims?"

> Then Kjartan started speaking and spoke to Bolli, “How
> willing are you, kinsman, to accept their faith which
> (the) king orders.

> Then Kjartan took to speech (ie started speaking) and
> spoke to Bolli: “How willing are you, kinsman, to accept
> their faith which (the) king preaches? (bjóða, Z5)”

When the pronoun doesn't refer to the subject of the clause,
the uninflected genitive of the personal pronoun is used.
For <þeir> that would be <þeirra>, not <þeirri>, so we must
have here the determiner: 'to accept the/that faith which
the king preaches/proclaims'. (<Þeirra> in the next
sentence, however, is 'their'.)

> Kjartan spyr: "Þótti yður konungurinn í engum hótum hafa
> við þá er eigi vildu undir ganga hans vilja?"

> Kjartan asks: "Did you think the king has not threatened
> them who would not subject (themselves) to his will?" (Z.
> hafa - h. í hótum við e-n, to threaten one)

> Kjartan asks, “Did it seem to you the king in any way
> threatens one, those who do not want to submit to his
> will?”

> Kjartan asks: “To you did the-king seem to make any
> (because of following eigi, see engi, Z2 (?)) threats
> against those who wanted not to go under (submit to) his
> will?”

I don't think that it's the following <eigi> so much as
simply the sense and normal English usage: we *could* 'seem
to make some threats', and it would have about the same
meaning, but it's less idiomatic than 'seem to make any
threats'.

> Er nú til stefnt öllum íslenskum mönnum.
> All the Icelandic men are now summoned.
> Now all Icelandic men are summoned.
> (It) is now summoned to all (the) Icelandic people (men).

Rob and Grace are right: <stefna til> 'to summon' takes a
dative object, so it's the Icelanders who are summoned.

> Konungur segir að þeir mundu þann kost velja sér til handa
> er þeim gegndi verr "eða hverjum yðrum þótti það ráðlegast
> að brenna mig inni?"

> The King says that they would each choose that alternative
> to which went against them worse "Who of you thought that
> advisable (?) to burn me to death in my house?"

> (The) king says that they will select a choice for
> themselves which to them goes worse, “or which of you
> thought it most advisable to burn me inside?”

> (The) king says that they would be-choosing on their own
> behalf that option which suited them worse (less) “but
> (see eða, Z4) to which of you seemed that most-advisable
> (superlative) to burn me inside?”

Or simply: '[The] king says that they would be picking that
choice for themselves that suited them worse'.

Brian