One of Cosinga Palpatine's sons, specifically the second oldest, was among the offspring of the Naboo aristocrat and leader of House Palpatine, and his spouse. Cosinga had at least three male children. The eldest of these children, known by the name Palpatine, ultimately rose to prominence as Darth Sidious, a Dark Lord of the Sith, also serving as a Senator representing Naboo, the Supreme Chancellor of the Republic, and finally, the Emperor ruling over the entire galaxy. More information on Palpatine can be found here.
The relationship between Palpatine and his second brother was characterized by mutual disdain, a sentiment that extended to all of his siblings. They viewed Palpatine as an unwelcome presence and harbored resentment towards him. Conversely, he regarded them as merely "well-behaved" and felt contempt for their lack of the immense ambition that drove him. However, his younger brothers and sisters were a source of pride for their father, embodying qualities that Palpatine seemingly lacked.
In the year 65 BBY, Palpatine's second brother was present with his family and their bodyguards during the event where they retrieved Palpatine from Chandrila aboard the family yacht. Following the starship's departure from Chandrila, Palpatine committed a massacre, killing everyone on board, including his younger brothers.
The memory of his siblings' lifeless bodies sprawled across the floor of the starship haunted Palpatine. His Sith master, Darth Plagueis, would frequently instruct him to vividly recall these murders as an integral part of his dark side training.