How twins differ even though same birth chart?
The 3rd house provides variations. effect differs according to it's nature
For eg:
If 3rd house lord is Saturn for twins,
But it represents benefits from older sibling. One is obviously older than other even if it's by few minutes.
Similarly, who they interact with differs from astrological point of view. If both get married, the nakshatras of their spouses will be different. Thus, providing different outcomes according to their interaction and social life with people around them.