This sounds like a great arrangement (I'm also not familiar with Castlevania's soundtrack) and great job performing. I think playing strings especially is a great skill since MIDI strings are always really hard to get sounding real from my experience.
From a mixing point of view, I think if you automated the volume of the violin vs piano at some sections where one or the other could take the foreground, that would stop it from overlapping a bit. Either that or you could pan them slightly off centre, one left one right.
Overall, cool track, good job. The arrangement is really cool.