> og slettir á sverðið.
> and smacks the sword with it (or smacks it with the sword??)

"smacks/slaps it with the sword" seems more the logical alternative...
Literally, as Grace translates: "and slaps the sword on (it)". In
other examples though, the object used to strike with is in the
dative, and the other online text of this saga has:

'Hon dró þá út brjóstit undan klæðunum ok slettir á beru sverðinu.'
"She drew out her breasts from under her clothes and slapped them with
the naked sword."

http://www.heimskringla.no/original/islendingesagaene/eirikssagarauda.php

But Gordon has:

'Hon tekr brjóstit upp ór serkinum ok slettir á sverðit.'

So presumably this is just an alternative possibility using the
accusative.

> Tveir menn féllu af Karlsefni en fjórir af Skrælingjum en þó urðu

þeir Karlsefni ofurliði bornir.

> Two men fell - of Karlsefni's but four (?) of the Skraelings - but

they (Karlsefni's band) overcame a greater force (lost that bit) [
and the CSOI seems to think more than four]

The other text has 'Tveir menn fellu af þeim Karlsefni, en fjölði af
þeim Skrælingum.' ("...many of the Skraelings").

'en þó urðu þeir Karlsefni ofurliði bornir'
"but Karlsefni and his men were overwhelmed by superior numbers"

'bornir' is the masculine nominative plural of 'borinn', past
participle of 'bera'. 'urðu' is the past 2rd pl. of 'verða', used
here to form the passive. 'ofurlið', neuter (older spelling: ofrlið)
= "superior numbers", "an overwhelming force". Synonymous with
'ofurefli' (older spelling: ofrefli), also neuter. 'ofurliði' is
dative singular, used in an instrumental sense.

LN