Well, Latvia and Lithuania are not Slavic in culture, save the culture pushed on to them via Russian domination. Their languages are related to each other, but are completely different to the Russian (and other Slavic languages) being in a different branch of Indo-European, with almost the same relationship as say, French and Dutch have with each other. Their folk culture has similar roots, but then so does the culture of say, Romania - another Eastern country in Europe that is not Slavic. I know a bunch of Latvians, and they are very different to the Poles, Bulgarians, Czechs and Russians I know, both ethnically and in attitude to life in general.
To be honest, even lumping the Slavic cultures together isn't really satisfactory, because even the Czech/Slovaks I know are culturally quite different to the Poles, and they are from a similar region in Europe and speak languages that are relatively close to each other.
Estonia is even less related. Their language is in a different language family, same as Finnish, and their culture is again very different to Russian.
To be honest, even lumping the Slavic cultures together isn't really satisfactory, because even the Czech/Slovaks I know are culturally quite different to the Poles, and they are from a similar region in Europe and speak languages that are relatively close to each other.
Estonia is even less related. Their language is in a different language family, same as Finnish, and their culture is again very different to Russian.