Quoting forgive-n let*love:" Say there is a Set of identical twin girls and a Set of identical twin boys (different families) they ... [snip!] ... combine with one egg, so there are MANY possibilies of DNA make up... regaurdless if its boy or girl. I hope that makes sense."
if two sets of identical twins got married and had kids, those kids, regardless of boy or girl, would appear as siblings on a DNA test.
you know how a DNA test can tell you how close two people are? like a paternity test can tell you if someone is your dad? the same test can tell you if someone is your cousin, or brother. except if both sets of parents are themselves identical twins, the cousins would actually look exactly like siblings do.
they would certainly NOT ever be identical. identical twins are the result of one sperm and one egg breaking in two, making two human beings. the chances of two siblings, or cousins, or any two people having 100% the same DNA are so small as to be actually as close to impossible as you can get.