> og mun þeim þó þykja þangað vor minni von
> and it will seem to them to-there is my expectation (??)

"the probability of us [going] there/that-way/in-that-direction will
seem less to them"
"they will not be expecting us there so much"
"they will think it less likely that we will go there"
"it will seem to them less likely that we will go there"
"the likelihood of us going there will seem less to them"

'minni' "less, smaller" is the comparative of 'lítill' "little,
small". It's feminine nominative here to agree with 'von'
"expectation, likelihood, probability" (which is just the modern
spelling of Old Norse 'ván'). Similarly, 'vor' is the modern spelling
of 'vár' "of us", genitive of the first person plural pronoun.
Complements of verbs and adjectives to do with wishing, waiting,
expecting, or asking for something are often genitive.

> Kári spurði Ingjald hver hann hefði særðan en hann sagði.
> Kári asked Ingjaldr who had (injured ?) him and he said.

That's right. 'særðan' is masculine accusative singular of the past
participle of 'særa' "to injure/wound". In Old Norse, the perfect
tense with 'hafa' can be formed in one of two ways. Either the neuter
singular of the past participle is used, regardless of the number and
gender of the object, or else the accusative form of the past
participle is used in agreement with the object. There's no difference
in meaning between the two forms.

(1) hann hafði sært marga menn (neut.nom./acc.sg.)
(2) Björn hafði særða þrjá menn (masc.acc.pl.)