Sentyabrina (Сентябрина, taken from the Russian word for
September / сентябрь as Oktyabrina is taken from the Russian word for October, октябрь) is a real name if very rare.
http://imenada.ru/sentyabrina/
I wasn't able to find anything on Rosewen, including no recorded usage of it in Wales. I suspect it is a variation of Welsh Rhoswen, or a combination of
Rose and the common Welsh name ending "wen". If not that, then it is possibly from another Brittonic language like Cornish or Breton.