Family Kamehameha (親子三大かめはめ波) is a much more powerful version of the Father-Son Kamehameha technique used by Goku, Gohan, and Goten in their Super Saiyan forms (though it is possible Goku's help may have been an illusion created by the Dragon Balls).
Gohan and Goten fire a combined Kamehameha at the opponent, who struggles against the attack. With the Dragon Balls in place, Goten wishes Goku was there. Thus, the spirit of their father Goku descends beside his two sons and transforms into his Super Saiyan form. Finally, Goku fires his Kamehameha as he, Gohan and Goten charge more power into the combined attack, overpowering the opponent and inflicting a huge amount of damage.
Goku, Gohan, and Goten use this attack against Legendary Super Saiyan Broly, who attacks with the Omega Blaster in the movie Dragon Ball Z: Broly - Second Coming. Though they manage to combat Broly in the Beam Struggle, Broly fires more energy spheres into his attack to blast it forward. As Broly prepares to destroy the Earth, an awakened Trunks fires his energy sphere at the Omega Blaster, preventing Broly from powering up his attack and causing it to weaken. Seeing their chance, Goku, Gohan, and Goten release all of their power into the Family Kamehameha. The attack makes Broly's Ki Blasts explode and breaks through Broly's Omega Blaster, blasting the Legendary Super Saiyan into the Sun.
Appearances in games
In Dragon Ball Z: Supersonic Warriors 2, the Family Kamehameha is performed like the Father-Son Kamehameha, with only Goku and Teen Gohan. In this same game, if Super Saiyan 3 Gotenks is in the team while Goku and Adult Gohan perform the Ultimate Kamehameha, Goten will also appear and shoot his own Kamehameha too.
Goku, Gohan, and Goten can also use this attack in Dragon Ball Z: W Bakuretsu Impact and Dragon Ball Heroes, in Dragon Ball Heroes their GT versions can also use the attack, made up of a 10x Kamehameha, a Super Kamehameha, and a Super Kamekameha.