Cozumel has dozens and dozens of private dive operators and instructors to choose from and they will most likely have arrangements for the whole family. It totally depends on the company and where they are located. Many do not have a shop, they are independent.
I can't personally recommend anyone, but if you google search the topic you will come up with lots of them to contact. We got certified in Cozumel with Papahogs in 2000, so many years ago. Just send out some e-mails to a bunch of them, and see what you find. A lot depends on your port time, too.