Two sisters were born on the same day in the same year, yet they aren't twins. None of their other sisters share the birthday. What's going on? Explain.
Having sister companies founded in the same day at the same is not unusual.
It's very similar to Colonel Panic's answer:
The two ladies are nursing sisters; their shared birthday is a coincidence.
In the same vein as Taemyr's answer, but reversed:
TL;DR: One Mother, possibly Two Different Fathers
Superfecundation: Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse. The term superfecundation is derived from fecund, meaning the ability to produce offspring.
Heteropaternal superfecundation occurs when two different males father fraternal twins.