They summoned the goddess Yogamaya and experienced her transfer the fetus from your womb of Devaki to the womb of Rohini (Vasudeva's other wife who lived along with her sister Yashoda across the river Yamuna, from the village of cowherds at Gokulam). Hence the kid conceived in a single womb https://ewr1.vultrobjects.com/blissdrive/SouthernCaliforniaSurrogacy/Becoming-A-Surrogate-In-Southern-California.html