CIO Twins - not working with one of the twins

I have already posted here a few days ago. I still feel so helpless. Our 12 month old twins are terrible sleepers. They have ever been, but for the last few weeks it has become absolutely horror. Twin A takes more than an hour, often even two to fall asleep and that only when being held and rocked. Twin B used to fall asleep a bit easier, took about 15 minutes do half an hour, but also only with being held and rocked to fully asleep, but then he wakes up every two hours during the night screaming his lungs out. I am so sleep deprived that my brain no longer functions properly and my shoulder is literally shattered from all the holding and carrying. As this was unsustainable, we finally gave in about two weeks ago and decided to CIO sleep train them. First night was horrible. Twin A screamed for 30 minutes but then fell asleep. Twin B screamed bloody murder for 2,5 hours before he finally fell asleep. The next day he half screamed, half fussed for half an hour, the third day he cried a little and mainly fussed for about 10-15 minutes before falling asleep and that is still the case. So basically he did learn how to fall asleep on his own, but his night wakings still occur every two hours or so. He still is nowhere near to sleeping through the night. The situation with the Twin A is even worse. After the first night's 30 minutes of crying, the next night it took him more than an hour, the third night he did not fall asleep even after two hours of screaming, so we've had to rescue it. We could not listen to him scream like that any more, which basically resetted the clock and we needed to train him from the beginning. We have just tried to do it again and I think he has recognised it and has started screaming like I'd never heard him scream before. He was crying literally out of his gut, he strained himself so much that he started throwing up and of course we had to stop and pick him up. He is now sitting in my husband's lap obviously awfully sleepy, but with no intention of falling asleep without the being held/rocked routine. The CIO method does not seem to work on him at all. I am desperate. They are too heavy to be held for hours without end. Also, I read all your posts about your one year old having 1,5 hour naps. My twins have never had a nap longer than 45 minutes in their life and even those they've had only a few times. Usually they have two naps during the day, each lasting 20-30 minutes. We have tried everything to change this, but with no success. The pediatrician is not concerned and says some babies just take longer to get the sleeping right. I am at my wits end and really do not know what to do anymore.