Calf scours - check into coccidiosis, it could be the cause. Scours can take down a calf quickly, and can be difficult to treat. You might want to talk to your vet if you give bucket calves another try, there are some meds you can keep on hand to give as soon as symptoms start.
But really, don't feel bad. People who have raised bucket calves their entire human lives still loose some. They can truly be a challenge...
And sometimes, people that sell bucket calves can be kinda like used car salesmen. You have to take what they say with a grain of salt. It is hard to know if the calves really got colostrum... It makes me wonder about his honesty, especially if he sold you TRUE twins without educating you... When you originally posted "twins" I assumed you were just saying it as a description, much like I call my dogs "siblings" when they have no relation at all, it's just a pet phrase because they are members of my family. I assumed you were calling them "twins" because they were the same age and appearance and from the same farm, not because they truly were from the same cow.
