Pathologist. The pathologist who conducted the autopsy would likely be the best person to contact to ask questions about the report. In some cases the family doctor or hospitalist can also answer those questions.
It is your right. You have a right, as the next of kin or other interested party, to have the autopsy report explained in layperson's terms. My reports always have a section that explains clearly to the family what the issues are and what we found. I had to stop talking to most families directly because of all the lawyers. I'm sorry for your loss and for the frustration and wish you luck getting things right.