Complex sentence: Grand Duke Paul wanted to recognize the child, who had been born legally as von Pistolkos son, and to marry Olga, but Tsar Nicholas II and Grand Duke Vladimir vehemently opposed their union.
Split into simpler sentences: Grand Duke Paul wanted to recognize the child who had been born legally as von Pistolkos son. He also would like to marry Olga, but Tsar Nicholas II and Grand Duke Vladimir vehemently opposed their union.