Princess Milica of Montenegro
Princess Milica Petrović- Njegoš of Montenegro, also known as Grand Duchess Militza Nikolaevna of Russia,( 14 July 1866 – 5 September 1951) was a Montenegrin princess.
She was the daughter of King Nikola I Petrović- Njegoš of Montenegro and his wife, Milena Vukotić.
Milica was the wife of Grand Duke Peter Nikolaevich of Russia, the younger brother of Grand Duke Nicholas Nikolaevich of Russia, whose wife was Milica's sister, Anastasia.
Princess Helen of Serbia
Princess Helen of Serbia and Yugoslavia (23 October (4 November New Style) 1884 – 16 October 1962) was the daughter of King Peter I of Yugoslavia and his wife Princess Zorka of Montenegro.
She was the elder sister of George, Crown Prince of Serbia and King Alexander I of Yugoslavia.
Helen was also a niece of Anastasia of Montenegro (or "Stana"), wife of Grand Duke Nicholas Nikolaevich of Russia, and of Milica of Montenegro, wife of Grand Duke Peter Nicolaievich of Russia, the women who introduced Grigori Rasputin to Tsarina Alexandra.
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Grand Duke Nicholas Nikolaevich of Russia (1831–1891)
Grand Duke Nicholas Nikolaevich of Russia (8 August 1831 – 25 April 1891) was the third son and sixth child of Tsar Nicholas I of Russia and Alexandra Feodorovna.
He may also be referred to as Nicholas Nikolaevich the Elder to tell him apart from his son.
Trained for the military, as a Field Marshal he commanded the Russian army of the Danube in the Russo-Turkish War, 1877–1878.
Grand Duke George Mikhailovich of Russia (1863–1919)
Grand Duke George Mikhailovich of Russia (23 August 1863 – 28 January 1919) was a son of Grand Duke Michael Nikolaevich of Russia and a first cousin of Emperor Alexander III.
He was a General in the Russian army in World War I. During the Russian Revolution, he was imprisoned by the Bolsheviks and shot by a firing squad, along with his brother, Grand Duke Nicholas Mikhailovich, and his cousins Grand Dukes Paul Alexandrovich and Dmitry Konstantinovich.
Duchess Alexandra of Oldenburg
Grand Duchess Alexandra Petrovna of Russia( tr.; Born Duchess Alexandra Frederica Wilhelmina of Oldenburg; 2 June 1838 – 25 April 1900) was a great- granddaughter of Emperor Paul I of Russia and the wife of Grand Duke Nicholas Nikolaevich of Russia, the elder.
Born Duchess Alexandra of Oldenburg, she was the eldest daughter of Duke Peter of Oldenburg and his wife Princess Therese of Nassau- Weilburg.
She grew up in Russia in close proximity to the Romanovs as her father was a nephew of Tsar Nicholas I of Russia.
Alexandra ’s parents were artistically gifted and passionate philanthropists.
They provided a good education for her and inspired in Alexandra a life of service to those in need.
Alexandra married in 1856, Grand Duke Nicholas Nikolaevich of Russia, the third son of TsarNicholas I and her first cousin once removed.
Alexandra, who had been raised in the Lutheran church, converted to the Orthodox faith, and took the name Grand Duchess Alexandra Petrovna of Russia.
The couple had two children: Grand Duke Nicholas Nikolaevich of Russia( 1856 – 1929), the younger, and Grand Duke Peter Nikolaevich of Russia( 1864 – 1931).
The marriage, arranged by the Russian Imperial family in an attempt to control the Grand Duke ’s excesses, was unhappy.
She was plain, serious and liked simplicity.
Deeply religious and very involved in charity work, Alexandra founded a training institute for nurses in St Petersburg in 1865.
The same year, her husband began an affair with a ballerina, forming a second family with his mistress.
After the collapse of her marriage, Alexandra lived separated from her husband who expelled her from their household in 1879.
A carriage accident left her almost completely paralyzed and, in November 1880, Alexandra went abroad to improve her health, compelled by her brother- in- law Tsar Alexander II.
The following year, she asked her nephew, Tsar Alexander III, to allow her to return to Russia and she settled in Kiev.
She recovered her mobility and, in 1889, she founded the Pokrov of Our Lady Monastery, a convent of nursing nuns with its own hospital, to provide free treatment for the poor.
She dedicated the rest of her life to the work at the hospital.
In 1889, she became an Orthodox nun under the name Anastasia.
She died at the convent in 1900.
Grand Duke Nicholas Konstantinovich of Russia
Grand Duke Nicholas Constantinovich of Russia( 14 February 1850 – 26 January 1918) was the first- born son of Grand Duke Konstantin Nikolayevich and Grand Duchess Alexandra Iosifovna of Russia and a grandson of Nicholas I of Russia.
Alexandra Feodorovna (Charlotte of Prussia)
Alexandra Feodorovna , born Princess Charlotte of Prussia (13 July 1798 – 1 November 1860), was Empress of Russia as the wife of Emperor Nicholas I .
Charlotte was the eldest surviving daughter of King Frederick William III of Prussia  and of Queen Louise of Prussia.
Her childhood was marked by the Napoleonic wars and by the death (1810) of her mother when Charlotte was just twelve years old.
In 1814 the Russian imperial family arranged her marriage – for political reasons – with Grand Duke Nicholas Pavlovich of Russia,
who later became Emperor Nicholas I.
The couple married on 1 July 1817.
Upon her marriage, Charlotte converted to Russian Orthodoxy, and took the Russian name "Alexandra Feodorovna".
Ideally matched with her husband, she had a happy marriage that produced a large family; seven of her children survived childhood.
Following the death of her brother-in-law, Emperor Alexander I of Russia, in December 1825, Alexandra's husband became the new Russian emperor.
Alexandra enjoyed her husband's confidence in affairs of state, but she had no interest in politics other than her personal attachment to Prussia, her native country.
She was the obedient and admiring supporter of her husband's views.
Her personality was completely overshadowed by Nicholas
I's strong character.
As empress, Alexandra Feodorovna had no interest in charity work.
Her chief interests were in family affairs, dancing, balls and jewels.
After 1841 her health deteriorated.
She spent long sojourns abroad in search of a respite to her illness.
As she became largely an invalid, Nicholas I took mistresses, but Alexandra retained her husband's love.
She survived Nicholas I by five years and died in 1860.
Grand Duke Nicholas Nikolaevich of Russia (1856–1929)
Grand Duke Nicholas Nikolaevich of Russia
( Russian: Николай Николаевич Романов( младший –" the younger"); 18 November 1856 – 5 January 1929) was a Russian general in World War I( 1914–1918).
A grandson of Emperor Nicholas I of Russia, he was commander in chief of the Russian Imperial Army units on the main front in the first year of the war.
He proved incompetent in strategy, tactics, logistics and coordination with the government.
The tsar took over his commands,
He later was a successful commander- in- chief in the Caucasus region.
He was briefly recognized as Tsar, Emperor of Russia in 1922 in areas controlled by the White Armies movement in the Russian Far East.
Catherine Chislova
Catherine Gavrilovna Chislova( Russian: Екатерина Гавриловна Числова)( 21 September 1846 – 13 December 1889) was a Russian ballerina.
She was the mistress of Grand Duke Nicholas Nikolaevich; they had five children.

Question: Who is Grand Duke Nicholas Nikolaevich Of Russia (1831–1891)'s maternal grandfather?
Answer: Frederick William III of Prussia