Almost identical twins

As the little girls grow up, your uncle and aunt never manage to know which one is Amy and which one is Andrea... or even if both are really girls.
You leave frequently and come back with bags of medicines and you receive packages of medicines you buy online from the beginning.

A reserch of the history of your computer shows you use to look for hormones and hormone blockers, so they guess at least one of the girls is not such...

They hope to get some final conclussion of which one is the boy few days after you gave birth as you start going out... but you've contracted a babysitter who won't allow them invading their intimity.

From time to time they even get a clue who is who as you say proudly that one of them as said her first word or had the first step... Even their voices even by then sounded very girly probably due tothose early hormones.

At that point they try to remember some differencies between them... but you make sure they always look the same... Even they both started growing their tits at the same time and to the exact same size. They suspect that was due to the hormones and due to their quite big DD size, maybe you even had to equilibrate giving hormones to the real girl since the fake one's tits had grown too much.

Asking them their names doesn't help either. They always have fun mocking of people making them confuse them so noone but their mother knows who is who.

It gets even worse when each year you give birth to more and more couple of twin girls... Britney and Brigitte, Charlotte and Claire, Donna y Danielle, Esther and Enid, Florence and Fiona, Gloria and Gina, Heather and Hope, Ingrid and Ivette, Jane and Jeanette, Kristine and Kendra, Lana and Laurel, Mandy and Mindy, Nancy and Nina, Pauline and Paola, Rachel and Ruth, Sarah and Sandy and finally the little Tammy and Tina.

Luckily for whole of you the three of your families were quite rich and with your old jobs you got lots of money... But the mistery remains: How many of the girls are really girls?

None of the girls asks anything about being different or wanting something different... At least with anyone that is not their mother.

Finally, one day, time after they got 18, one of the first girls comes to see the couple, "I want to know the truth."