system
Given the following post, respond as if you're commenting on Reddit:
human
Given two sets of twins (male and female). If each pair has a child, can you determine which child “belongs” to what parents purely from a DNA test?

As the question implies, if you have two sets of twins (male and female) and each pair has a child, of the same sex or different sex, would you be able to tell what child “belongs” to what parents?

If each dad and mom shares identical DNA with their twin, wouldn’t these children (who are cousins) be genetically identified as siblings? And in addition, can you tell if there’s any genetic difference between identical twins?
gpt
Short answer is no, they are genetically siblings, and parentage can't be deducted.

Long answer is sometimes.  Even identical twins may not have identical DNA (e.g. non-zero chance for identical twins to be different genders or for one to have a trisomy the other doesn't). Telomeres, transcription errors, and crossover may be able to differentiate parentage.

Outside DNA, microbiota from birthing, immune system cell transfer from feeding, and skin colony from cosleeping could be used to differentiate with whom they were doing these activities.