Witches of St. Petersburg by Imogen Edwards-Jones

Sisters Militza and Stana fight their way through the Russian court using spiritualism, charm, black magic and manipulation of the Tsar and Tsarina. They married into the court but learn quickly that the way to power is to control Tsarina Alexandra. With every daughter born, Alexandra becomes more despondent and willing to try any magic or listen to any religious charlatan that the sisters send to her.
This is a different side of the Romanov court where incredible waste and riches gave way to superstition and desperation. When the sisters discover Rasputin they unknowingly unleash a monster that could mean their downfall. Politics, history, court gossip and the incredible sexual escapades of Rasputin are all shared in great detail. The author has spent time doing her research but there were times I wanted to skim to get to the action.