1.
<Nation name="Russian" chance="10">
<FirstName>Sasha</FirstName>
<FirstName>Misha</FirstName>
<FirstName>Kolya</FirstName>
In Russian, Sacha is diminutive ('pet') form for name Alexander, Misha - for Michail, and Kolya for Nicolai.
Such forms can be used in conversation between friends, or family members, or when spoken about children, but practically never in official papers.
I think it's mostly improbable to see such names in soldier duty roster.
Ergo -
<FirstName>Alexander</FirstName>
<FirstName>Michail</FirstName>
<FirstName>Nicolai</FirstName>
2.
<Nation name="Ukranian" chance="2">
<FirstName>Stilyan</FirstName>
<FirstName>Lazslo</FirstName>
Stilyan is Bulgarian name, not Ukrainian. Lazslo is not Ukrainian name too.
3.
Practically, Russian and Ukrainian firstnames are the same, maybe with minor difference in pronunciation.
Xenonauts events taking place in 1979 - so both Russian and Ukrainian soldiers are from Soviet Union, and their credentials where in Russian.
Maybe it's worthwhile just to join/duplicate both firstname lists?
PS. Russian is my native language, and several years of my childhood (in mid-1970s) I spent in Kiev, Ukraine