I have the same problem.
We are booked to DC for April and I emailed them and asked their advice. You are OK to wear glasses for the dolphin swim although they suggested securing them with a sweatband. I thought I would wear an old pair of sunglasses attached to one of those coloured straps, then if they get lost/damaged it won't be the end of the world.
For the snorkelling they have a selection of prescription masks that you can hire, so it would be an idea to take a note of your prescription with you - it would save trying all the masks on!!!
Elaine