If they were a real alliance they would nominate 1 each of their members to each pair of nominees. They would always have the numbers toevict anyone they want. But they aren't a true alliance because they don't trust each other to go on the block.
God how I hope Devin doesn't have more crazy last-minute plans and throws anyone new in the mix now, though the houseguests are really bringing it on themselves for going along with everything he does. The "Bomb Squad" need a revolt before disbanding.