My husband also has liver issues from CF. About 20% of CF patients have liver problems associated with the CF. My husband has been taking actigal for years. He sees a liver doctor annually to make sure that things are still okay.
One thing to be aware of is that some of the doctors don't think that about the liver complications and prescribe medications that can hurt (like pain medications), so if the liver is a concern, make sure to keep the doctors on their toes about that stuff!
Also, another complication that can come with the liver issues is low clotting factors and platlet counts, which can be complicated. So, just keep that in mind as well.
It is good that they are finding out now so that your son can start on the medication to hopefully halt or at least slow down the progess (actigal) and you can be aware of the issues so that you can keep the doctors in line. I would also insist that your CF doctor send you to a liver specialist. CF doctors, in my experience, are too "lung" focused. Centers have liver docs that are involved, so it shouldn't be a problem.