Past Housemates
 

If they past housemates going in just become normal housemates for this series, they have a huge advantage and most likely all of them will make the final. Why not wait for an All stars or soemthing?
Plus they'll get 100% of camera time and the actual housemates of the series will be invisible.
Saying that, what a waste if they're only there for the task, just leave it all together

They're only in the house until the following eviction.