> alla hina dauðu fyrir það er þeir fóru með þann hug til fundar við

þig að

> veita þér ákomur
>
> all the dead for it that they went along with that idea to fight

with you

> and your brothers to grant? you ??

ákomur, acc.pl. of ákoma/ákváma "wound" (can also mean "touch"):
"because they went with intent to wound you."

> Tyrfing í Berjanesi og skal hann selja þér sök á hendur Önundi í

Tröllaskógi

> er mál á eftir Egil bróður sinn."
>
> Tyrfing in Bear's Nose and he shall hand over to you a case

(against) Onund

> in Troll's Forest which case (he?) has regarding Egil, his brother.

I think the relative 'er' refers to Önundr, rather than 'mál', thus:
"who has a case (to bring) for (the killing of) his brother Egill."
MM & HP: "whose duty it is to take action over the killing of his
brother."

LN