They'd kill each other lawl. There would be no getting along without a common enemy because they are WAy too similar. Two queens in one kingdom so does not work! Plus, Queen Mab wouldn't take well to a human sorceress acting like she is an equal lol. Because I know dear Regina would bow to no one, including a goddess.
Click the eggs! --> "We thought we'd come in the traditional way...through the door."---"It's traditional to open it first."