Grandduke Wilhelm Ernst was the grandson of grandduchess Sophie. Her (only) son was Karl August Wilhelm Nicolaus Alexander Michael Bernhard Heinrich Frederick Stefan, Hereditary Grand Duke of Saxe-Weimar-Eisenach (31 July 1844 - 20 November 1894).
Because his mother was a daughter of King William II of the Netherlands and his older uncles, except King William III, died childless, Karl August was next in line in the succession to the throne of the Netherlands. He was preceded (after the death of crown prince Willem and Alexander) only by the young Queen Wilhelmina. This was the reason for him learning to write and speak fluent Dutch, due to the possibility of Karl August becoming king if Wilhelmina died childless.
Karl August died at Cap Martin, France, six years before his father; because of this, his eldest son Wilhelm Ernst succeded his grandfather as Grand Duke. In Friedrichshafen on 26 August 1873 Karl August married with Pauline of Saxe-Weimar-Eisenach. They were distant cousins, as she was the granddaughter of Bernhard, younger brother of the Grand Duke Karl Frederick of Saxe-Weimar-Eisenach, the grandfather of Karl August.
Karl August and Pauline had two sons:
Wilhelm Ernst Karl Alexander Friedrich Heinrich Bernhard Albert Georg Hermann, Grand Duke of Saxe-Weimar-Eisenach (b. Weimar, 10 June 1876 - d. Heinrichau, 24 April 1923).
Bernhard Karl Alexander Hermann Heinrich Wilhelm Oscar Friedrich Franz Peter (b. Weimar, 18 April 1878 - d. Weimar, 1 October 1900).
I checked my books and found the follwing about the Sachsen Weimars.
Wilhelm Ernst was heir apparant tot the Dutch throne but in the Netherlands it was assumed that he would not give up his throne as grandduke of Sachsen Weimar Eisenach menaing he could never become king of the Netherlands (the Dutch constitution forbids the king or queen to be bearer of another crown thad the Dutch one).
Wilhelm Ernst was described by count Dumonceau (from King William lll 'court in The Hague) as "a strange personage, not very favorable in his looks , little and rather fat. When he speaks it is in staccato, emphasizing every word in a strange way. He seems to be not very intelligent but at the same time could make impression with his knowledge". Countess van de Poll (lady in waiting of queen Emma) states the following "the heriditary grandduke is a little, ugly and noisy man. He made me feel ucomfortale during dinner. He yelled loudly at me from across the dinner table that he had heard that I (the countess) could fluently speak German which he found odd".
His brother, prince Bernard was described as not very intelligent and sickly and therefore by no means suitable as a king to be. His nickname at the Dutch court was "the Sachsen Weimar monster".
The event of which you speak about grandduchess Sophie is that she warned her father King William ll about the riots having found place all over Germany in 1848 including against her own court in Weimar, which had scared her very much. In the Netherlands there were hardly any riots at at that time but when a few citizen made their complaints to the King he was feared so much that he immidiately agreed for a new and more liberal constitution.
King William lll and his sister dsliked each other and Queen Sophie of the Netherlands nearly hated the grandduchess and found her unreliable and disgusting. The grandduchess herself was a cultivated woman and had a keen interest in the development of Sachsen Weimar. She was also very generous adn helped her country in every way she could. She inherited the legacy of Goethe and Schiller and took the greates care of this legacy. She had built an own institute to house this legacy and shared it with the rest of the world. But she also could become extremely furios about simple things. The grandduchess shared these "attacks of anger and fury" with her brother King William lll who had the same character and owned his nicname "King gorilla" to his fury. When things were not going the way he wanted he could easily shout out that the "guilty ones" should be hanged immdiately or something like that. Even queen Emma was afraid of his fury and that is why she refused to become regent at the first ilness (the king was mentally declining and not capable of reigning) of her husband. She feared him becoming furious by the time he would have a clear mind and would recognizedwhat his wife had done.
Queen Sophie of the Netherlands already described in 1876 (one year before she died) that the Dutch crownwould go to this terrible woman in Weimar. At that point her two remaining sons still lived. King William married Emma allthough his sons could not agree with this marriage.
