How does the genetic material differ between dizygotic twins and ordinary siblings?
Differences in genetic material between dizygotic twins and siblings are likely to be very similar.  


  Dizygotic twins, or so-called fraternal twins, on the other hand, are no more genetically similar than any other set of siblings. - Utah.edu


Since all oocytes are all synthesized during fetal development, dizygotic twins are no more likely to come from a single mitotic division than siblings are.

Also note that in human females, only one egg comes from the a full mitotic division: