Of course China could build two carriers in different yard concurrently - technically. But money is also an issue, carriers are not cheap. The Chinese defense budget has never seen any single procurement that expensive ( not even SSBN's).
Not just the building of the carrier that is expensive. Are the Chinese equipped with enough fighters to be placed on top of both carriers (new one + Liaoning), are the Chinese already equipped with enough knowledge and skills in operating a carrier (its SOP from cooking meals to firefighting to whatever), do the Chinese have enough escort for all their carriers, do the Chinese have comprehensive training with the entire fleet?
Of course the Chinese had the money now, but they might need more time with training of the crews and pilots and the overall system before comfortably launching more carrier.
But since there are evidence (not sure how accurate) that the Chinese are already building the next carrier, I have this feeling that at least 1 batch of trained crews are about to be completed, and these crews could be put on the new carrier.
As of such, i have this nagging feeling that the newest carrier will be an update of the Liaoning, so that the crew needed less time to be familiarise with the latest carrier operation, while catapults will be installed into this new carrier to train more crews and pilots on the catapult operation, so that the third carrier can removed the ski jump and progress to pure catapults only. Just my 2 cents though.