> "Við förum kynlega með okkur um málin,"

'We proceed strangely between ourselves concerning the (our)
speeches,' (we´re not really saying what´s on our minds?)

I don't remember meeting this expression in a similar context, so I
can't add anything useful here; but as far as I know, you're right,
except that I'd have thought 'um málin' was "about these matters (this
business)". MM & HP paraphrase: "Let's not beat about the bush."

> Jarl lét dæma Hrapp útlaga (note indecl adj)

Or it could be the accusative singular of the noun 'útlagi'; compare:
'doema e-n skógarmann'.