við þar sem (I can´t follow the syntax here))
One of the meanings - CV - gives to þar sem  is which so that seems to read
við þar sem would mean - with which... things had come (about)
Þorvald was his son - he may have been pleased withall that Silver
rífka svo ráð fyrir dóttur þinni
in Zoega  it has to improve (or it could be repair) your daughter's standing
Hrut may have the view that since Hallgerð was dissatisfied with the
marriage - and was the cause of Thjostolf's actions - people may think
ill of her in connection with this - makes sense ??
Er sá einn til (?)    I could all easily be wrong - but I saw this as "it is seen"   "it is seen - that"
like the speaker is stating the obvious
I hope i have helped Alan - for so much help you have been to me