Here’s my translation

Alan

Síðan ríða þeir báðir bræður vestur til Helgafells. Þorkell tekur við þeim
After-that they, both brothers, ride west to Helgafell. Þorkell receives them

með allri blíðu og þau Guðrún bæði og buðu Þorleiki þar að vera um veturinn
with all friendliness and they (he and) Guðrún both also invited Þorleikr to be (stay) there during the-winter

og það þiggur hann. Þorleikur dvelst að Helgafelli um hríð, ríður síðan til
and he accepts that. Þorleikr stayed at Helgafell a while, rides afterwards to

Hvítár og lætur setja upp skipið en flytja vestur varnað sinn.
Hvítá (White-River) and causes to draw-up the-ship (ashore) and conveys his goods west.

Þorleiki hafði gott orðið til fjár og virðingar því að hann hafði gerst handgenginn
For Þorleikr (it) had become (pp of verða) good for (ie he had acquired) wealth and honour because he had become attached-as-retainer

hinum tignasta manni, Ólafi konungi. Var hann nú að Helgafelli um veturinn
to the most noble person (man), King Ólafr. He was (stayed) now at Helgafell during the-winter

en Bolli í Tungu.
but (and) Bolli (stayed) in Tunga (Tongue)

71. kafli - Viðurtal þeirra bræðra
Chapter 71 – (The) Conversations (viðrtal, probably plural, given what follows) of those brothers

Annan vetur eftir útkomu Þorleiks finnast þeir bræður jafnan og höfðu tal
(The) next winter after Þorleikr’s coming-out (to Iceland) those brothers constantly meet-one-another and had conversations (the sense suggests –tal is the acc plural form)

með sér og hvorki hentu þeir gaman að leikum né annarri skemmtan.
between themselves and they took delight (see henta gaman at e-u under henta, Z1) neither in sports nor other amusements.

Og eitt sinn er Þorleikur var í Tungu þá töluðu þeir bræður svo að dægrum skipti.
And one time when Þorleikr was (stayed) in Tunga (Tongue) then those brothers talked such that (it) changed in astronomical (half) days (note: not dagr but doegr, Z1 or Z2, whose to know?, ie for at least the 12 hours either side of midnight, days and nights together, given Snorri´s comment below)

Snorri þóttist þá vita að þeir mundu stórt nakkvað ráða. Þá gekk Snorri á
Snorri bethought-himself then to know that they would be-planning something (see nökkurr) big. Then Snorri went to

tal þeirra bræðra. Þeir fögnuðu honum vel og létu þegar falla niður talið.
(the) conversation of those brothers. They greeted him well and (but) caused at-once to drop (lit: fall down) the-conversation (object, accusative).

Hann tók vel kveðju þeirra.
He received well their greeting.

Síðan mælti Snorri: "Hvað hafið þið í ráðagerðum er þið gáið hvorki svefns né matar?"
After-that Snorri spoke: “What do you-two have in plans (ie what are you guys up to, scheming) when you-two heed (gá) neither sleep nor food?”

Bolli svarar: "Þetta eru ekki ráðagerðir því að það tal er með litlum merkjum
Bolli answers: “These are not plans because that conversation is of little significance (merki, Z3)

er vér eigum að tala."
(of) which we have to speak.” (seems a little self-contradictory to have to speak of thing of little significance)

Og er Snorri fann að þeir vildu leyna hann því öllu er þeim var í skapi en
And when Snorri perceived (past) that they wanted to conceal all that which was in their mind(s), (not sure what the particle en is doing here)

hann grunaði þó að þeir mundu um það mest tala er stór vandræði mundu af gerast
he suspected nevertheless that they would be-talking mostly about that, from (af) which (er) large troubles (plural) would come-to-pass

ef fram gengi. Snorri mælti til þeirra: "Hitt grunar mig nú sem það
if (it) should-go forward (proceed). Snorri spoke to them: “I suspect (impers mik grunar, under gruna, Z4) (the) other (ie the opposite, hinn, dem pron.) now, that (sem, Z6) that

muni hvorki hégómi né gamanmál er þið munuð lengstum um tala
will (be) neither nonsense nor joking that you-two will be-talking most-of-the-time

og virði eg ykkur til vorkunnar þótt svo sé og gerið svo vel og segið mér og leynið mig eigi.
and I pay-heed-to you to what-is-to-be-excused (várkunn) with you-two  (ie I consider this excusable with you, I don’t blame you) even-if (it) should-be so, and please (lit: do so well and, imperative) say (imperative) to me and do-not-conceal (imperative) from me.

Munum vér eigi allir verr kunna um ráða þetta mál því að eg mun hvergi
We all (ie you-two and I) will not worse be-able to (kunna+ inf) resolve (ráða, verb) this matter because I will by-no-means

í móti standa að það gangi fram er ykkar sómi vaxi við."
stand against (oppose) that that goes forward (proceeds) when the-honour (sómi, noun) of you-two should-grow with (it).”

Þorleiki þótti Snorri vel undir taka. Sagði hann í fám orðum ætlan þeirra
Snorri seemed to Þorleikr to go-along-with (it) (cf þau tóku undir þetta léttiliga, to second, under taka, Z12) well. He said in few words (the) intention of those

bræðra að þeir ætla að fara að þeim Ólafssonum og þeir skyldu sæta
brothers that they intended to go at (ie attack) those sons-of-Ólafr and they (ie Ólafr’s sons) should suffer (sæta, Z2)

afarkostum, segja sig þá ekki til skorta að hafa jafnan hlut af þeim
hard-terms, (they) say themselves then (ie at that time) not to-be-in-want-of (that), to have an equal standing (hlutr, Z6) with those

Ólafssonum er Þorleikur var handgenginn Ólafi konungi en Bolli kominn í
sons-of-Ólafr when Þorleikr was attached-as-retainer to King Ólafr but (and) Bolli connected

mægðir við slíkan höfðingja sem Snorri er.
by affinity-by-marriage with such a chief as Snorri is.