Sorry about your husband's and your suffering. CC is very difficult for all involved because it is a nasty and sneaky disease. The issue of a negative biopsy is a well known one. My dad went through 2 or 3 biopsies, they were all negative. The reason is that the tumor sits in the "porta hepatis", i.e., the center of the liver right between the main hepatic bile ducts, adjacent to all the large vascular structures (portal vein etc). This makes the biopsy very very difficult and dangerous. The brushings they get via endoscopic approach many times yields insufficient amount of cells to make a diagnosis.
The diagnosis, as far as I know, is many times based on the constellation of clinical presentation, lab findings, ERCP (endoscopic exam) and/or MRCP (magnetic resonance cholangiopancreaticography). When they see the mass in the porta hepatis with erosion of the hepatic bile ducts, even in the face of a negative biopsy or brushing, doctors are willing to accept the diagnosis. This is my understanding based on my personal experience with my father's disease.
For me, the hardest part with the diagnosis was acceptance particularly because the specialists told us what was going on, but with the negative biopsies we were hoping for an alternate diagnosis. This resulted in wasting a month or so running around pursuing dead ends while treatment should have been administered. So, I sympathize with your situation. It is a very very difficult one.
Just to tell you a little bit of my dad's case, which may be helpful to you in the future, shortly after diagnosis he received 2 stents in the bile ducts. This made passage of the bile possible again and releived his congestion and resulting jaundice. Then he received radiation (no chemotherapy, we decided against it at the time). He did very well for 4-5 months, but then started having infections (liver abscess, that spread to his lung and ended up killing him 12 months after diagnosis). He was offered surgery in the very beginning, that was clearly the only chance at curing the disease, but the odds were 15% cure vs 85% major complications and/or rapid return of the disease - he did not want to play those odds...
I hope your husband does better. Wish you the best of luck.
PS: this email is based on my personal experience and my own readings and research. It does not represent expert opinion or medical advice. It may not be applicable to your husband's case at all depending on his diagnosis, stage of disease, etc.