Cool. You've said while jotun is a fairly unique language they are quick to pickup other languages without much worry. This explains it when Jotun names aren't quite as brutal as their language, so norse names can easily fit.

I'll break down the name I choose, which is Bjornolfr "Gnýn" Steinnbiarnarssonr Naglnjortas. What a mouthful. Anyway, gnyn is an inherited nickname, I figured raiders, explorers, and sailors would need short and direct names that are easy enough to be spoken by foreigners. The relationship between bjornolfr and steinnbjornr( the bjorn suffix in a surname becomes biarnar-) is pretty obvious really( Can't have ulfbjorn or it would have been that). The relationship between Naglnjortr and steinnbjornr is from rhyme though- I imagined Naglnjortr having an enormous brood to his wife and multiple concubines that they ran out of alliteration and variations and so had to start rhyming.