Considering they take on "colorful nicknames" would lead me to believe they either don't have surnames in the traditional sense, or that said surnames are of little importance in comparison to one's deeds.
Like your example, Erikson. One would think a Highlanders chosen nickname would be what they would be referred to more than their first name. As it is their reputation. So having Erikson on the end would likely bring little honor or glory to the individual, as his father, Erik, would have been likely more known by his title name.
However, this doesn't necessarily mean it's a rule. The most important NPC Highlander is Raubahn Aldynn. And so, unless there's some old lore that mentions his surname of Aldynn, it doesn't really seem like a title, or a family name, or whichever.
So I'd say it's still pretty open in terms of interpretation.
Like your example, Erikson. One would think a Highlanders chosen nickname would be what they would be referred to more than their first name. As it is their reputation. So having Erikson on the end would likely bring little honor or glory to the individual, as his father, Erik, would have been likely more known by his title name.
However, this doesn't necessarily mean it's a rule. The most important NPC Highlander is Raubahn Aldynn. And so, unless there's some old lore that mentions his surname of Aldynn, it doesn't really seem like a title, or a family name, or whichever.
So I'd say it's still pretty open in terms of interpretation.
