right? remember the chapter when our attention was directed to the older brother bringing food to the younger one in the nursery. "Why are *you* bringing it?" "Because I helped make it!" (oh dear) Right afterward we're shown little brother coughing in bed and the older one bringing him warm milk--and *insisting he not tell Tanaka about it*. The next day, after having partaken twice of food/drink Big Brother brought him, Little Brother is so sick he can't go on the boat trip. That's just the kind of evidence Sherlock Holmes would zero in on, haha.
I have a sneaking suspicion that Big Brother also had something to do with the family tragedy, like arranging a scenario in which he could step in and rescue his little brother ("mummy thinks you would look very impressive!" asdslaksdfgh good job, Mom), but because he was just a kid it all went horribly wrong and backfired: "I'm an utter failure of a son and heir." And the way he compared their tenant farmers to 'sheep', yikes. Even Vincent was a little >_>
We kept hearing about how weak and fragile the younger twin was, but Our Ciel was actually the stronger, more independent twin all along. He had a healthy view of himself as a separate being and accepted that he and his brother would naturally have their own lives as they grew up--he was looking forward to it, in fact, and even had a highly unique and original plan for his own future rather than the traditional path for younger sons of titled families. It was the elder brother who could not countenance their ever being parted. Yandere backstories Inc. XD
If the older brother wasn't Munchausen-by-Proxying the younger one, I'll eat my Easter Bonnet, LOL. Remember how often he brought him food/tea/warm milk, etc.? "I helped make it! <3" Yeah, I'll bet you did. The extra ingredient is *yandere*.