Ah, sleep training twins... My oldest slept through the night at 8 weeks (12 hours), my ds was still waking twice a night for bottles at 6 months. It took us 2 nights to Ferberize him, and then he was sleeping for 12 hours straight, plus 2 solid naps. My next dd slept through on her own at 4 months.
Therefore, with my twins, we put dd's crib close to the door, and ds's on the other side, thinking that, because he was a boy, we'd be plucking him up. Turns out he was a great sleeper, his twin not so much. Finally, at 6 months, we realized that we'd have to Ferberize them both (she'd cry, wake him up, they'd both cry). Only took a weekend, and after that, they'd easily sleep through each other's crying, for several years. Turns out ds still needs at least an hour more sleep than dd.
All of mine are great sleepers, even when we travel. Now that they're older, everyone sleeps past 9 on the weekends.
As for the OP, I am a strong CIO supporter, but not at 8 weeks. I don't think one should CIO that young.