How is it that Maxim, Lyudmila, and Diana have three Bubuki amongst them?
The character biographies on the show's official website (http://bbkbrnk.com/character/04/) provide an explanation for this unusual state of affairs.


Maxim: 「ブランキ“ザンパザ”の「心臓」を父親から受け継いでいる。」 ― that is, he inherited Zampaza's heart from his father. 
Lyudmila: 「ザンパザの右手にあたるブブキ“シュヴェドッカ”を母親から受け継いでいる。」 ― she inherited Zampaza's right arm from her mother. 
Diana: 「母の双子の妹（叔母）の死後、主人無しとなっていたザンパザの左手にあたるブブキ“ズヴョズダチカ”を受け継いでいる。」 ― hers is the weird case. Her mother's younger sister passed away (presumably without any descendants), so Zampaza's left arm took Diana (her former master's niece) as its master instead.