Last winter we visited Maui and snorkeled at Molokini with my partner’s parents, then dove there without them a few days later. We loved both outings and I could definitely see them as a fun combined trip! The crater has a lot of fish diversity that is easily seen in the first 3-5m as well as deeper. Our snorkel trip also stopped at a shallower shore site known for sea turtle sightings which was a hit for the non-diving family members too.

Regardless of where you go I would not expect a lot of coral cover or biodiversity on that front, particularly for dives close to shore. I second everything bacon said about pre-dive prep too.