My fiance and I are having our approved Roman Catholic Ceremony at EDR's chapel on October 29th. It is actually not as complicated as it might seem, although there is TRULY a lack of information out there so I don't blame you for being skeptical! We had a couple of resorts tell us that we could have a "Catholic" ceremony on the beach which we knew wasn't valid, so we waded through a lot of information until we found one or two resorts that had approved chapels (Grand Palladium is another, also beautiful! Their chapel is actually much prettier but over all we liked the EDR resort best).
Essentially, you will need to complete Pre-Cana at your parish here, and go through the interview process with your priest and witnesses (he just confirms that you and your fiance are free to wed, ie never married or marriage annulled). This is standard for a Catholic wedding no matter the destination. This then gets sent with your birth certificates (and confirmation certificates - US Diocese don't require this for marriage but Mexico does) to your local Archdiocese, who stamps it's validity and sends it to the Archdiocese of Quintana Roo.
EDR has a priest that they routinely work with for Catholic ceremonies and they provided me with his e-mail address so that my fiance and I can communicate with him beforehand (he speaks English/Spanish). Unfortunately since he has his own parish he can't do a rehearsal the night before, but we can do that with the wedding coordinator and it's a small price to pay for being able to have a beautiful destination wedding that is also valid in the Catholic Church!
Beware of "renting" priests online to show up at your wedding and perform it for you - I wouldn't trust that they are truly Catholic!
Please message me if any questions, I would be more than happy to help you out if I know the answers!!! Best of luck!!!