It sounds like you'd be more or less a co-founder. Why are you only getting 10% and not 1/3? Do you really think their "idea" is worth that much? Ask for 1/3 an

It sounds like you'd be more or less a co-founder. Why are you only getting 10% and not 1/3? Do you really think their "idea" is worth that much? Ask for 1/3 and align your interests with the other co-founders if you really want to do this.