Are they identical?

Almost certainly not.  We've never cared about the answer to this one, but at various points the health care professionals told us it was unlikely but they couldn't rule it out.  (Apparently, the fact they were dichorionic and diamniotic was not dispositive of the issue, because all fraternal twins are dichorionic, but not all dichorionic twins are fraternal, or something like that.)  We also know that the weight differential at birth isn't enough in itself to rule it out, nor is their apparent differences in appearance (which might be attributable, we are told, to weight alone).  We heard a rumor that they have different blood types, which would be a pretty conclusive answer to the above question.