Nestor the Chronicler's Повѣсть времѧньныхъ лѣтъ (lit. Tale of Bygone Times, but usually translated from Old Eastern Slavic as The Russian Primary Chronicle) was published in 1113 and is probably the best primary source to answer this question, but even within that text, minor deviations and definite extrapolations are present. This is the first, and among the only contemporaneous histories of the region though, so that's why you have modern historians debate about who did what with respect to settling the land that would become Russia. This is the heart of the Norman and anti-Norman argument.

So who founded Holy Mother Rus? The Chronicle has this to say (emphasis mine):

"To the lot of Japheth fell the northern and the western sections... He likewise acquired dominion over other rivers, among them the Desna, the Pripet', the Dvina, the Volkhov, and the Volga, which flows eastward into the portion of Shem. In the share of Japheth lies Rus', Chud', and all the gentiles... The Varangians dwell on the shores of that same sea [the Baltic Sea], and extend to the eastward as far as the portion of Shem [another son of Noah]. They likewise live to the west beside this sea as far as the land of the English and the French. For the following nations also are a part of the race of Japheth: the Varangians, the Swedes, the Normans, the Gotlanders, the Russes, the English, the Spaniards, the Italians, the Romans, the Germans, the French, the Venetians, the Genoese, and so on. Their homes are situated in the northwest, and adjoin the Hamitic tribes." (pp. 51-52)

Quick biblical refresher here, Japheth was the son of Noah and one of the supposed inheritors of the earth after the Great Flood. This text was published in 1113 as I mentioned earlier, which is about 120 years after the Christianization of the Kievan Rus' (988), so it's understandable that by this point, Eastern Slavs are now chronicling their history from biblical times. I don't think it's an overreach to say that modern historical study has discredited that part of the excerpt as obviously untrue, but the latter part of the bolded portion mentions the Varangians, that's the bit which is important here because this is the beginning of the story of the people who inhabited ancient Russia. The Varangians were a people of Scandinavian origin who traveled inland via the Neva river from the Baltic Sea (in modern-day Saint Petersburg) and ultimately settled the area that would become the Kievan Rus'.

So the time periods we're talking about here are the late 8th and early 9th centuries, which (debatably) mark the ethnogenesis of the people who would go on to become Russians, Ukranians, and Belorussians (after a fashion). I say debatably because there are some historians who postulate that the people living in the lands that would be conquered by the Varangians were organized in some kind of a Khanate of Rus before the formation of the Kingdom of Novgorod, but even those that put forward that idea acknowledge that the rulers of such entities were also genetic Norsemen. So okay, even if the Varangians weren't the first overlords of Rus, and they destroyed all evidence of their predecessors, those guys were also vikings of some stripe which further supports the Norman (derived from the word Norsemen or Northmen) argument.

I'm obviously not familiar with the exact books you're talking about, what claims they make, or what you specifically have issue with, but anyone trying to claim the Varangians are not historical figures or that they were not of Scandinavian origin has their work cut out for them. The Varangians are well-attested in plenty of primary historical sources, including those outside the region (such as the Byzantine Empire).

As to whether or not Rurik was a historical figure, the debate becomes a lot more interesting. Nestor's Russian Primary Chronicle is the only source in which such a figure is mentioned. Specifically (emphasis mine):

"After two years, Sineus and his brother Truvor died, and Rurik assumed the sole authority [over their lands]. He assigned cities to his followers, Polotsk to one, Rostov to another, and to another Beloozero. In these cities there are thus Varangian colonists, but the first settlers were, in Novgorod, Slavs; in Polotsk, Krivichians; at Beloozero, Ves', in Rostov, Merians; and in Murom, Muromians. Rurik had dominion over all these district." (pp. 60)

Direct support of the Norman claim. There you have it: according to Nestor-- the Varangians were Normans. They ruled over Slavs. This was the formation of the kingdom of Novgorod. Novgorod is the same kingdom Rurik's supposed great-grandson Vladimir (now Saint Vladimir) Christianized 100 years later.

But are we sure that Vladimir was truly a descendant of Rurik? The Chronicle isn't the only source for that claim, but it is the main one. Here is the supposed lineage:

• Rurik
• Ingvar (Slavified as Igor) of Kiev
• Sviatoslav I of Kiev
• Vladimir the Great

So four generations back to Rurik. One doesn't have to suspend a ton of disbelief to think that Nestor was able to access sources to support that claim, even if they no longer exist today.

Just to throw a monkey wrench into the conversation and show (again) why this is still a matter of debate:

"Igor' [is] soundly attested, presumably with dates, by the treaties with the Greeks in which [he is] mentioned by name. The chronicler could thus work back from these treaties and attach the subjects of tradition, wherever possible, to a related item of Greek chronology. Regarding Igor' he had no material apart from the fact that he was Rurik's son." (pp. 34 of the Introduction written by the translators and editors of the text in 1953)

So, apparently it's not just an open and shut case as some would have you believe. Indeed, the source for Rurik's existence is only the claim of the second person in that chronology above, Ingvar or Igor. It gets worse. Igor is attested to have ruled for 31 years (914-945) by Nestor, but the treaties mentioned above with the Byzantines as well as the Chronicles itself make no mention of specific deeds of Igor until the 940's. Also from the Introduction:

"In the reign of Igor', the Varangian Russes are again distinguished from Polyanians, Slovene, and Krivichians (anno 944), and once more, in the treaty of 945, a list of names is supplied of which the majority are not Slavic, but Norse" (pp. 40)

So now we're trusting the guy who may not have even ruled for the years Nestor claims. That means that we have a historical document which makes a then-common but now-debunked claim about the inheritance of European and other lands by a person called Japheth, followed by a shaky claim about a figure called Rurik who consolidated and ruled Novgorod, which is only supported by his son-- whose own history is also a matter of debate.

I think the answer to your first questions is that the Norman argument is supported much more by the historical record, but the second (about the figure Rurik) is still rightfully a matter of debate.

Here's a link to the complete text of the Russian Primary Chronicle.