There is more to co-habiting species than just the same food and environment. As Aimless said, they do not have the same requirements. A water pool suitable for the frog will make it too humid for the leos.
Fire-bellied toads are toxic. If they feel threatened, they'll secrete toxins from their skin, which can also wash off in the water dish. Your leopards might lick him, since leos are fond of licking their surroundings. Even if they leave him alone, he will no doubt feel threatened by the much bigger lizards living so close to him. He'll be constantly secreting his toxins, and it will end up in the water dish, since he'll be soaking in there often.
You leos will be extremely sick, and most likely dead, in no time.