The difference between the spellings hryvnia and hryvnya for the Ukrainian гривня is one of English transliteration, specifically how to transliterate the Ukrainian Cyrillic letter я. In both transliterations the letter before the "a" does not represent a separate syllable, but only the softening (palatalization) of the "n". Other possible renderings would be "hryvnja", "hryvňa", "hryvn'a", and "hryvña", since the letter "j", the caron, the apostrophe, and the tilde are all conventional ways (in separate systems) of indicating such palatalization. Curiously, the Oxford American Dictionary gives "hryvna" as its main headword (despite indicating the iotization of the a in its pronunciation guide), with "hryvnia" as an "also". (I can understand why it might make sense to reserve the y-transliteration for the Ukrainian vowel "y"/"и", though the same argument can be made for preserving "i" for the Ukrainian vowel "i".)
LesHerasymchuk is right, though, about the history of the Ukrainian language: both Ukrainian and Russian (as well as Belorusian) come from Old East Slavic (the language of the medieval state known as Kievan Rus); Ukrainian does not come from Russian. In terms of continuity, it is more accurate to say that Russian comes from Old Ukrainian (though linguists don't usually use that anachronistic term, preferring instead "Old East Slavic"). And it is also true that Russian was profoundly influenced by Church Slavonic, a by-product of Old Bulgaro-Macedonian (a South Slavic language). I don't know whether modern Ukrainian has been as deeply influenced by Church Slavonic.