So, Danyl and Miss Frank were the worst performers on the night? No.
Lets think about who was voting. The ordinary voter over the age of 25 would perhaps vote once, and select, in their opinion, the best performer on the night (but with a little of the previous performances taken into account). Who would be the bulk of the voters, and how many times would they vote for the same act on the same evening? I would suggest the 12-18 age range, predominently girls, and perhaps voting many times via their mobiles. Therefore, would they vote for a cute 16yr old lad who they 'fancy' or a chap who is over 25? Would they also vote for a female singer who they could aspire to sing like, or perhaps see themselves as?
Now the main question is why are the twins still there? Well, they are anti-heros. Hated by many, yet some would vote for them because they may find them entertaining, or perhaps 'rocking the boat' so they keep voting them in. I personally find them an irritation, and they have no place on the show at this stage because they cannot sing, cannot dance affectively and appear to have a bad attitude. I prefer voting for talent; the type of talent I could listen to in concert or on CD. Not talentless individuals offering me no personal enjoyment or long term international success.