When it comes to their personal life they both often talk about their mother, but I've never seen either talk about their father (many suspect they have different fathers due to their difference in appearance). I would not at all be surprised if they are half sisters raised solely by their mother (with both fathers being estranged) and Pavel has became an almost father like figure to them, in fact, that is what I suspect.
While trying to find more of Valentina's early fights, I got lost in the Russian part of the 'net. Which is where I found out that Antonina and Valentina share the same patronymic name (Anatolievna) so with the way Russian naming conventions work they have the same father, who by the way was named Anatoli. So they are full biological sisters.
Her training partner is cute too.