> 1. Again, I'd love to find out more about these names and their
> meanings, please: Þrándr/Þorlákr

Þrándr/Þróndr is thought to be related to the verb 'þróa'.

> 2. tvá sonu = Modern Icelandic tvo syni, I guess. This is what I would
> expect in a way, it's just that I thought plural numbers took the
> genitive singular in Modern Icelandic and Old Norse, e.g. fimm manns
> (five men).

Sometimes, yes, but not always!

> 3. fríðr sýnum, handsome to the sight(?) - I'd have expected the
> singular, but maybe as he appealed to the sense of sight of lots of
> people…..

The word sjónir/sýnir can be literally 'eyes' as well
as the more abstract 'sight'.

> 4. Þrándr var ok með því­ móti: þetta er hebreska fyrir
> mér!:-)

The word 'mót' means something like 'form, mode, way'.
Þrándr var ok með því móti...
Þrándr was also with that form...
Þrándr was also the same way...

Kveðja,
Haukur