They have power over themselves and their actions, they have little or no power or real influence in the country. They're certainly not making it in any way fascist. In fact the only reason they have any standing at all is due to the Russian aggression, if the Russian's hadn't invaded Azov would be truly irrelevant.
However, with a lot of fascists rewarded with government posts after their performance in maidan and an entire fascist batallion somehow having the independence to defy a presidential order to stand down in a war, it's pretty clear that fascists hold a significant level of power in Ukraine.