I guess the question is: are we here to pay respects to our Father, and ensure our extended, not-hugely close family can pay respects too...
Or are we here to recruit them to our vengeance?
I think if we're doing the former, the latter option of 'let IF just handle it' is fine. We announce who we are, we announce our father's death and how he died bravely, killing 40 men, and we go on our way.
If we want to reveal everything, how we have used our Seidr to determine our family's ally in our home betrayed us, and paid to have Steinnar assassinated, and that we seek people to join us to burn down his home and kill him for that crime, we might be best to do the former, and find a cool/smart way to plan out what we would want of them.
We have no proof as of right now of Dorri's crimes, but this is clearly a very... powerful group of people, if they have dozens of warships and some of them can fit 100 oars. They probably have enough forces to crush Dorri if we pointed them at Hading. But what would be left might be... questionable. Same with if they would believe us.