Kom heill!

Thank you for the letter. These are exactly the sort of
questions I was hoping to get.

> djúpauðga - what is the grammatical significance of the GA ending,
> if any, please?

We have the masculine noun 'auðr' which means 'wealth'
and an adjective formed from that word 'auðigr' meaning
'wealthy'.

The inflexion of 'auðigr' is explained here:

http://hem.passagen.se/peter9/gram/g_adj_st.html

> What are the other cases of the female name Ólöfu (here seemingly in the
> accusative)?

nom. Ólöf
acc. Ólöfu
dat. Ólöfu
gen. Ólafar

> What is the nominative and the exact meaning of Götuskeggja (here acc.
> pl.?) It seems to be something like Streetbeard (or Gata beard), but
> surely that can't be right!

Correct on all accounts.

Götuskeggjar
Götuskeggja
Götuskeggjum
Götuskeggja

I don't know why they were called Streetbeards :-)

Kveðja,
Haukur