> En þó að því sé að skipta og segir þú það satt að annaðhvort sé að

eg drepi þá eða þeir mig þá vil eg miklu heldur þola dauða af þeim en
eg geri þeim nokkuð mein. En þú ert maður að verri er þú hefir þetta
mælt."

> but should it turn out - I say truly that if I kill them or they

(kill) me then will I greatly prefer to endure death from them than do
them harm, But you are the worse man that you have said this" [got
badly stuck here]

You got it more or less right, just watch out for 'segir þú það satt'
"you are telling the truth".

"But should it turns out that you are telling the truth [in such a
way] that it should be (i.e. should happen, come about) that either I
should kill them or they [kill] me, then I would much rather endure
death from them then do them any harm. But/and you are the worse a man
(you are a worse man) for having said this."

'að verri' (the) worse (cf. því verri).

> En eg varð þess vís að honum þótti þú hafa haft við sig fjörráð
> And I have learned this that he thought you would have killed him

Yes, lit. "I became aware of that, that he thought [...]" 'þess' is
the genitive of 'það'. It anticipates the subordinate clause (þess =
að honum þótti þú hafa haft við sig fjörráð), so it's also possible to
leave it out of an English translation, and just say: "And I have
learnt that he thought you meant to kill him".

I suspect that "I learnt this, that he thought [...]" makes the
translation more emphatic than the original.