"First, you all can die, and this matter will end. But the positive side of this option is that I will not harm the rest of your clan." Before, Aditya planned to wipe out this entire clan and only leave the young and the women of the clan alive.
But knowing that the rest of the clan wasn't involved, he changed his mind. But Elder Isshin is the only one who won't be receiving any of his mercy.
The first option made them feel like an invisible hand was squeezing their hearts.
"Second, I will only kill Elder Isshin and the rest of you will sign a soul contract agreeing to not reveal our identities in any shape, form, or manner." The moment everyone heard the second option, everyone knew what to choose.
The death of one Elder was way better than the better of the remaining elders. If all the Elders of the clan died today, then there is no way that the clan will be able to survive against the six remaining clans.