Woah woah woah, so you are keeping the male and female siblings together in one cage, AND then putting a third one in the same cage with the other male and the female?
Even if its just for mating season that is just plain stupid, and extremely dangerous too.
You really need to double think your current set-ups before you do any of this.
And just because they are brother and sister doesn't mean they have to be together. Its not healthy and it just screams bad husbandry.