When is your anniversary? The Caymans are currently closed to all foreign tourists unless you quarantine and there is pretty mixed messaging on when that will change. Some think as early as this summer, some seem to be saying not until late fall. I would take anybody saying anything definitive about the situation with a grain of salt, as there have been several planned reopening dates that have subsequently been pushed back, and the currently "plan" seems to be based on achieving a population vaccination % goal that seems to be a bit of a moving target that they are not close to achieving.
I have not been to Southern Cross Club, but they are a well regarded resort and I have never heard anybody unhappy with their stay there. There are really only 3 resorts on the island, Southern Cross is most known as a "barefoot luxury" type of place, a little more expensive, but they take good care of you. Little Cayman Beach Resort is where we have stayed many times, and it is a great place to go and dive and relax. Nothing ultra luxurious about the rooms, but they are clean, well updated, and very convenient to the dive shop and restaurant. Pirates Point is a little more quaint, and used to be owned by a professional chef, who I believe passed away a few years ago. The experience there was less diving focused and more focused on the good food, and I believe pre-covid they had several chefs sharing the duties there. Not sure what they will be doing when things reopen.
There is decent snorkeling out around Owen Island that would be reachable from SCC with a kayak, otherwise most of the best snorkeling is going to be on the north side of the island along the Bloody Bay Wall or at the east end around Point of Sand. Both of which would require a bike ride, moped rental, or car rental to reach from SCC.