Love the names! They're some of my favorite Slavic ones. Though I think Nikolay is much better spelled
Nikolai. I feel like the spelling you put would be confusing to Americans.
Borislav is one of my brother's favorite names. I agree it's way cool. I love both
Alexei and
Ilya, though I don't they flow well in this combo unfortunately.
Aleksy (the Polish spelling -- I'm Polish) is on my shortlist.