You have to remember when dealing with the Nordic races:
1. That the Normans occupied Sicily in 1068 and were barely two generations out of Norway. Magnus was another two generations later, I don't think anyone has a good genealogical record of his ancestry. 2. Also, the Haithabu Roerik of Dorestad may have been the Konung of Novgorod (late 9th C). His great grandson married the sister of Basileus II: one may presume any descent worked the other way as well. This is simply indicative of the common experience, see the Project Gutenberg translation of Cynewulf's Elene as a worked example of a Varingarian writing up details of a pivotal period of history from his English Saxon viewpoint to see that the traffic along the Volga went both ways! 3. Genealogies in maritime families must be taken with a huge pinch of salt. The wife at home was not in receipt of salaried income, indeed she was uncertain if she'd ever see her husband again, and so many scheduled their marriages - note the plural - to ensure that hubby on ship A was never in port at the same time as hubby off ship B. This week she was Mrs Wilkes, next week Mrs Johnson.
In practical terms, you're also most unlikely to find any hard genealogies, as any Scottish records would have been destroyed by the English in the aftermath of the 1745 uprising. The Portsmouth Mains have a better reputation from c1820 onwards, as they acquired some social standing, but suffice it to say the family which remained in Portsmouth fitted in two generations for every one in those who moved away since the 1950s - average age of first birth 16-17 versus 35.