> Eg mun ríða drottinsdaginn og svo nóttina með.
I think `svo...með' here = "too" or "as well": "I will ride during the
Lord's Day (Sunday) and the night too."
> Skuluð þér þá þar allir komnir er eiðsvarar eruð við þetta mál.
"You should then all have come/arrived [all you] who are oath-swearers
in this case/matter." (Past participle, with the auxiliary `vera'
omitted.)
> þá skal engu fyrir týna nema lífinu
Lit. "then shall nothing be lost except the life" i.e. "then we
won't inflict any penalty less than taking that man's life". See CV
under `fyrir' "instead". There's another instance of the expression,
also from Njála, quoted there: `þér skulut öngu fyrir týna nema
lífinu', for which is offered the translation "you shall lose nothing
less than your head".