There is a so-called Baltic language family, which includes Latvian and Lithuanian (and mostly extinct other dialects like the pre-German original Prussian). This is thought to be related most closely to the Slavic family (though, again, the notion of a simple family tree ignores mixing). The main languages further north (Estonian, Finnish) are of the Finnie branch of the Finno-Ugric language family, thought to be the result of a wantering from the Urals across the far north. Though, again, there was probably substantial mixing, which is undeniable in the case of the also Finno-Ugric Sami [Lapps] whose genetic analysis shows a strong local component with at least 5,000 years of separate history.

BTW, Ukrainian nationalists like to emphasize that the Muscovite Rus assimilated a significant Finno-Ugric population, thus they believe Ukrainians as successors to the population of the Kievan Rus are more properly Slavic than Russians. (Which is also funny, considering all the nomadic people moving through the are of modern Ukraine from east to west who mixed with the Slavs there.)

_{*Lunatic*, n.
One whose delusions are out of fashion.}