> Hrappur hleypur þar að sem þeir eru fyrir Njálssynir.
> Hrapp leaps there to where? they are before Njall's sons.

"H. runs up to Njall's sons." Or more literally: "H. runs to where
they, Njall's sons, are present."

'hleypur að' "runs (up) to"
'þar...sem' "where" is relative (=þar...er).
'fyrir' "present" (adverbial here, rather than a preposition).
'þeir' "they" = 'Njálssynir' (nominative, thus not the complement of
the preposition 'fyrir').
'þar...sem þeir eru fyrir' "where they are present", i.e. "where they
are".

Some similar examples:

Hann gekk þar at, sem þeir Oddr ok Ásmundr hvíldu
"He goes to where O. and A. were resting"

Hon gékk þar at, er Guðríðr sat
"She goes to where G. was sitting"

hann hljóp þar at er Hildr var fyrir.
"he ran to where H. was."

Hróaldr Özurarson hljóp þar at, sem Skarpheðinn var fyrir, ok lagði
til hans.
"H. runs to where Sk. was and thrust at him."

[...] ok gengr þar at, sem einn steinn stóð.
"[...] and goes to where a certain stone stood."

Finnbogi gengur þar að sem einn steinn mikill stóð jarðfastur.
"F. goes to where a big stone stood fixed in the earth."

> Hann mælti: "Bjargið mér góðir drengir
> He spoke, "Save me (you?) noble-minded (men?)

Yes, 'bjargið mér' = 'bjargið þér mér' "save me" (2nd person plural
imperative), and 'góðir drengir' "(you) gallant/brave/noble-minded
fellows/men".

> "Það mundi eg vilja," segir Hrappur, "að þið hlytuð af mér mest illt."
> "I would wish it,"says Hrapp," that you get from me most bad (M & P

have ill luck)."

Yes. 'hlytuð' is the Modern Icelandic 2nd person preterite
subjunctive of 'hljóta' = Old Icelandic 'hlytið'.

> "Menn erum við til þess," segir Helgi, "að launa þér það þá er

stundir líða."

> "We are men (enough?) for this," says Helgi, "to repay you then that

as time goes on."

I think that's the idea: "We are such men as will be able to pay you
back for that in (due) time." 'þess' is the gentive of 'það' = "að
launa þér [...]"

> I wondered if the previous remark by Gudbrand was supposed to show

his faith or that he was naïve.

I agree with Patricia: definitily a dig at Gudbrand's naivety. One
parallel that comes to mind is Ögmundar þáttr dytts [
http://www.snerpa.is/net/isl/dytts.htm ], which pokes fun at the
people of Sweden for gullibly ascribing human abilities (and
desires...) to a statue. Presumably both of these annecdotes are also
a satire on heathen faith in general; I can't think of any similar
annecdotes told of Christian believers in Old Norse literature.

LN