With respect to Strel'nikov, the question is a very contentious one. Some people think he is just an anti-hero (Antipov, his real last name, is a clue to this), who fights Zhivago's "life" with executions (Strel'nikov is based on the word for shooting in Russian). Others for some bizarre reason associate him with Sokol'nikov, who was a minor Bolshevik - I don't know why, though - everything about Sokol'nikov is different from who Strel'nikov is. The last name just sounds similar. Others think he is Marshal Tukhachevsky, executed by Stalin. Given Pasternak's protection by Stalin, many see Yevgraf as Stalin. The forest partisans are based on a variety of groups of red partisans that Pasternak researched and read about when he was living in Yekaterinburg in the Urals.

Yuri's family seems to be a blend of lower nobility and the merchant class (the "kuptsy" ). The merchant class arose in the 18th Century and by the 19th Century many of them were fabulously wealthy. Their code of honor was paramount to them, and if they shook hands on something they would abide by the terms of the agreement as scrupulously as if they had signed a written contract. As they became extremely wealthy, many of them married into impoverished noble families to increase their pedigree (a practice common all over Europe at the time). It seems that the Zhivagos on the father's side were kuptsy, and the mother's side were impoverished nobles. The Gromekos are the exact same way - the combination of the factories and country homes shows a mixture of enterprise and privilege.

Greg is completely right that by today's standards (and indeed, by Soviet standards) they would be considered part of the intelligentsia.

That question shows that you don't really know Russia well. Russia has always controlled the movement of its people. The peasants were tied to the land, and after the Revolution the Bolsheviks enslaved them once again by instituting a system of internal passports and not giving them to the peasants. Without an internal passport, it was impossible to board a train or take a commuter bus to a different town or stay in a hotel.

Even if a person had an internal passport, however, they still needed an external passport to travel. Getting an external passport was a very difficult process, and even now it can be complicated and frustrating. In the Soviet period, however, it raised questions about loyalty and people had to prove they were good Party members or that they were at least committed to Soviet ideals, to get a passport. Even with an external passport, it was not possible to leave the country without travel papers. It was almost impossible to get these travel papers - trips were viewed with extreme suspicion, even to places like East Germany, KGB minders were attached to groups to spy on them and keep them from fleeing and upon their return they were forced to detail every hour of their trip and explain any suspicious contacts they might have had. If the authorities were not happy about the responses, they might never give someone travel papers ever again.

The Soviet Union did not have a habit of exiling dissidents until the 1970s. Prior to that time, it was considered dangerous to let potential enemies out of the country, where they could publish the truth about what life in the Soviet Union was like. As a result, internal exile (or, in the 1930s, summary execution) was preferred to giving travel papers to people critical of the Soviet system.