> Nú leikur mér það eigi í hug að á yður hallist um vor viðskipti
> our dealings are lacking (?)

"I'm not thinking that there will be an unfavourable report about you,
as regards our dealings."

> Hitt er heldur að mér þykir illt ef að er spurt að þér hafið engi
jól verri haft en þessi er nú koma í hönd."
> it is held to me to think ill if it could be said that you have had
a Yuletide as poor as the one now coming (in hand)

In this case, 'heldur' is the comparative adverb meaning "rather",
rather than the verb 'halda' "to hold". "It (the cause of my mood) is
rather that I will think it ill if it's found out that you've not had
a worse yule than this one which now is coming."

> Eg þykist finna að þú ert nokkuru fálátari en verið hefir,
> It seems to me that you are somewhat silent (Z-fá-latr) than you
have been

Comparative: "somewhat quieter than", "rather less talkative than"

> að menn þóttust trautt slíka rausnarveislu séð hafa.
> that men thought there had never been such a noble-feast (?)

'trautt' = "hardly, scarcely, barely". So you could maybe translate
it as something like: "that people thought they'd hardly seen such a
magnificent feast" (although that sounds slightly odd in English). I
suppose we might express it by saying that they could hardly remember
seeing such a fine feast, or they could scarcely believe that there'd
been ..., or didn't believe that they'd seen many feasts as
magnificent as that one.

> og kvað góða frétt af honum
> and said Good News would come from him

"and said (in support of his marriage proposal) that he'd heard good
things about him."

> og lét hún það sitt ráð sem Eiríkur vildi
fyrir sjá.
> she let see Eirik's advice as he wished her to see

I think it's saying: "and she said that her decision (what she would
do) would be what(ever) Eirik wanted to arrange" -- i.e. if she would
agree to what he thought best.

> laungetna

"illegitimate, begotten out of wedlock", presumably not literally a
secret in this case.

> Hann var heldur við aldur, ódæll
í skapi,
> old and cranky?

Nice way of putting it!