Sorry I've fallen behind with the comments. Been a bit busy of late...

> En hann var vistlaus og kona hans. Nú voru þau eftir að skipi tvö

nokkurar nætur. Þá var enn ung kristni á Grænlandi.
But he and his wife were without a Home (Vistlaus ? - Homeless)

> Now they were back at the ship for two nights. Then (it was at that

time when) Christianity was young in Greenland.
[is this supposed to explain the lack of accommodation - "No room at
the Inn]

Possibly, although my guess is that it could just as easily *not* be
meant as an explanation of the lack of hospitality, more a sort of a
"oh by the way, did I mention, the Christian faith was still new to
Greenland" - as if the writer, or whoever added these words, was
reminded of the fact by the anecdote they were just beginning. So it
could be an explanation in advance of the sinister goings on that are
about to be recounted.