The Sons of Feanor came to Beleriand after the rebellion of the Noldor in Aman, and established realms in East Beleriand. They waged unceasing war on Morgoth, aiming to recover the Silmarils, and after Beren and Lúthien's quest won one Jewel, turned against their fellow Elves. Celegorm, Caranthir and Curufin died during the Kinslaying at Doriath, Amrod and Amras at the Havens of Sirion, and Maedhros and Maglor were lost at the end of the First Age, having retrieved their Silmarils but lost the right to them.
Celebrimbor son of Curufin was the last surviving descendant of the House of Feanor. He lived on into the Second Age and created the Rings of Power.
Gondolin RPG began after the Nirnaeth Arnoediad, by which point the Sons of Feanor had lost their lands in the North and taken to a wandering, nomadic existence. Celebrimbor, an earlier arrival by the Hidden Way, had settled into the city and made some friends, despite his Feanorian status, before the Fall.
The first encounter between the surviving Sons of Feanor and the inhabitants of Gondolin took place during the scouting expedition, when Turgon, Halatir, Telperina and Heledir encountered Amrod and Amras after a warg attack. Turgon met and spoke with his cousin Maedhros during their stay in the camp, and after the scouts' departure, they were followed by the twins.