Definitely use the Weill Cornell Connect, it's the best way to reach the doctors. It's all in writing, you can take time wording your questions the way that you want to and then you can read the responses. All your son's medical records are there. It's the only way that I communicate with my GI outside of office visits. I usually have a reply within a few hours.
https://mychart.med.cornell.edu/mychart/default.asp
I remember when Hep-C meant that you would eventually need a liver transplant, now with recent medical breakthroughs there is a 95% cure rate. PSC is a slow moving disease, it could be many decades before Jeff would need a transplant.