Here’s my translation

Alan

Guðlaugr hét maðr. 
[There] was a man called Guðlaugr

Hann var Valentínusson. 
He was a son of Valentína.

Hann bjó á bæ þeim, er hét at Stökkum. 
He dwelled on that farm, which was-called at Stakkar (Stacks of Hay)

Jólinn hét systir Guðlaugs. 
Guðlaugr´s sister was-called Jólinn

Hana átti Ingi. 
Ingi had her [in marriage].

Þat var eitt haust, þá er sauðir váru reknir saman í rétt at Rauðasandi, at Markús lét draga sauði sína í hús til skurðar. 
That was one autumn, when sheep were driven together (ie rounded up) into [the] public-fold [used for the regular-autumn sheep-gathering] at Rauðasandr (Red Sand), that Markús caused to draw (ie guide, shepherd) his sheep into a ‘house’ [ie farm-building] for slaughtering (slaughterhouse I).

Þá kómu þeir Guðlaugr ok Ingi til réttarinnar. 
Then they Guðlaugr and Ingi came to the public-fold.

Þeir fengu til mann þann, er Þormóðr hét, at draga sauð þann, er Ingi átti, til sauða Markúss, þeira er til skurðar váru dregnir, því at þeir vildu gefa Markúsi gagnsök í móti fjárheimtu þeiri, er hann heimti bænhústollinn at Inga. 
They got (cf fá e-n til at göra e-t, fá, Z12) that person (man), who was-called Þormóðr, to draw (ie guide, shepherd) that sheep, which Ingi owned, towards [the] sheep of Markúss (ie to induce it to join the flock, draga e-en til e-s, Z10) , those which were drawn (ie had been shepherded in) for slaughtering, because they (Guðlaugr and Ingi, not the sheep) wanted to give Markús a counter-charge in-return-for that claim-for-money-owing, when (er, Z.ii.2 or whereby, er, Z i.3,) he (Markúss) claimed the house-of-prayer (chapel)-toll from Ingi.

Síðan skildust menn at réttinni. 
After-that people (men) parted-company from the-sheep-gathering-[fold].

En um morgininn eftir fekk Markús menn til at skera sauði þá, er inn váru dregnir. 
But (And) [the] next morning after Markús got (cf fá e-n til at göra e-t, fá, Z12) people (men) to slaughter those sheep, which were drawn (ie had been shepherded) inside.

En er húskarlar Markúss váru at slátra, þá sendu þeir Ingi mann til fundar við þá at vita, hvárt þeir hefði skorit sauðinn, þann er Ingi hafði látit draga til sauða Markúss, en þeir Markús vissu enga ván til, at Ingi átti þar sauð inni með sauðum Markúss. 
But (And) when [the] man-servants of Markúss were slaughtering (verb, inf), then they, Ingi [and Guðlaugr] sent a person (man) to see (lit: a meeting with) them (the house-servants) to find-out, whether they had slaughtered the-sheep, that-one (singular) which Ingi had caused to draw to (induce to go among) [the] the sheep of Markúss, but (and) they, Markús [and co] had (lit: knew) no expectation of [it], that Ingi owned a sheep inside there among [the] sheep of Markús.

Þá höfðu húskarlar Markúss skorit sauðinn. 
Then (ie by that time) [the] house-servants had slaughtered the-sheep (sg, ie Ingi’s sheep, singular)

En þá er sendimaðr Inga kom þangat til, er þeir slátruðu, þá heilsuðu þeir honum, en hann tók kveðju þeira. 
But (And) when [the] messenger of Ingi came thither to where they slaughtered, then they (the man-servants) greeted him, but (and) he received their greeting.

Hann tók upp höfuð sauða þeira, er þeir höfðu skorit, ok finnr þar höfuð þat, er mark Inga var á, en þeir svöruðu ok kváðust eigi vitat hafa, at með því marki hefði verit. 
He took up [the] heads (neut plural) of those sheep, which they had slaughtered, and finds there that head (neut sg), on which was [the] mark of Ingi, but they (the man-servants) answered and declared-of-themselves not to have known, that [it, the sheep’s head] had been with that mark.

Sendimaðr Inga fór í brott ok kemr á fund þeira Guðlaugs ok segir, at húskarlar Markúss hefði skorit gelding, er Ingi átti. 
[The] messenger of Ingi journeyed away and comes to a meeting of them, Guðlaugr [and Ingi] and says, that [the] man-servants of Markús had slaughtered [the] wether, which Ingi owned.

Nú er Markús varð þess varr, at húskarlar hans hefði skorit sauð þann, er Ingi átti, þá sendi hann mann til fundar við þá Inga ok Guðlaug ok bauð at gjalda fé fyrir sauð þann, vaðmál eða sauð þann annan, er þeir vildi, ef þeim þætti sér þat betr koma at hafa heldr en slátr þess sauðar, er skorinn var. 
Now when Markús became aware of that, that [his] man-servants had slaughtered that sheep, which Ingi owned, then he sent a person (man) to see (lit: to a meeting with) Ingi and Guðlaugr, and offered to repay property for that sheep, wadmal or that other (ie another) sheep, which they wanted, if [it] should-seem to them that to have come better (ie if they should think that that was a better outcome) for themselves, rather than [the] flesh-meat of that sheep, which was (ie had been) slaughtered.

Þeir svöruðu ok kváðust ekki vilja þat þiggja, er Markús bauð.
They answered and declared of themselves not to want to accept that, which Markús offered.