First off... Sunwing sucks.
Secondly, I don't think you have a very good TA --- you need to find yourself a TA that specializes in destination weddings. The one I used was fantastic, and secured rates for a much longer period than 7 days.
We knew (100%) sure that we had 30-40 ppl going to Cuba -- this was our immeadiate family that had guaranteed us. So we put the deposit down for them (yes out of our own pocket), and our TA managed to double the space with Air Canada vacations. We paid deposit for 40 ppl, ACV held 40 more spaces, and by the end of the booking process we actually ran out of secured spaces.
What I am suggesting is this, secure the number of spaces you KNOW you will be utilizing, get your TA (or find one that will) increase the hold on extra spaces so that you may secure a rate for your guests.
Ciao A.