I may be out of line with this, but would it be possible to take them to an appt with your pdoc and have your pdoc explain things? They might have a better understanding of the complexities (even if they don't end up actually understanding the particulars). It's a lot for someone on the outside to grasp, and people tend to oversimplify things they don't understand.

Of course, if you don't have a good relationship with them, and your pdoc doesn't know in advance what your intent is, then this would not be a good option. I also like the suggestion above for them to go to a family support group.