From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Family Kamehameha (親子 三大 かめはめ波, Oyako Sandai Kamehameha; Literally meaning "Parent-Child Three Generations Turtle Destruction Wave") is an energy wave attack used by Son Gohan, Son Goku, and Son Goten in their Super Saiyan forms.
First, Super Saiyan Gohan and Super Saiyan Goten fire a combined Kamehameha at their opponent, who struggles against the attack. With the Dragon Balls in place, Super Saiyan Goten next wishes that Goku be present. The spirit of Goku then descends beside his two sons and transforms into his Super Saiyan form. Finally, Super Saiyan Goku fires his Kamehameha as he, Super Saiyan Gohan, and Super Saiyan Goten charge more power into the combined attack, overpowering their opponent and inflicting a huge amount of damage.
Super Saiyan Goku, Super Saiyan Gohan, and Super Saiyan Goten used this attack against in their fight against Broly in his Legendary Super Saiyan form in Dragon Ball Z: Broly: Second Coming. Though they managed to combat Legendary Super Saiyan Broly in an Energy Struggle, Legendary Super Saiyan Broly fired more energy spheres into his attack to blast it forward. As Legendary Super Saiyan Broly prepared to destroy Planet Earth, an awakened Trunks Brief fired his energy sphere at the Omega Blaster and prevented Legendary Super Saiyan Broly from powering up his attack and caused it to weaken. Seeing their chance, Super Saiyan Goku, Super Saiyan Gohan, and Super Saiyan Goten released all of their power into the Family Kamehameha and broke through his Omega Blaster, blasting the Legendary Super Saiyan into the Sun where he was apparently destroyed by the solar flames.
- The Family Kamehameha has many similarities with the Father-Son Kamehameha. Both techniques and their respective enemy's energy attacks (Omega Blaster for Family Kamehameha and Solar Kamehameha for Father-Son Kamehameha) were repeatedly charged during their respective energy wave struggles, both received help from a Z Warriors' energy sphere (Trunks for Family Kamehameha and Vegeta for Father-Son Kamehameha), and both techniques killed and blasted their enemies up into outer space (while this occurred in the Father-Son Kamehameha's case with Super Perfect Cell, the Family Kamehameha simply blasted Broly up at space into the Sun, where he was then killed.