It's best to just stay with the kids and go to Margaritaville.
In our case, we showed up around 8pm (peak time) and had to wait half an hour. They gave us a beeper and we walked around taking pictures and the girls went into the shops while I got a drink.
Then we went into the restaurant, the food was awesome, the girls liked the atmosphere, even if they didn't have a clue who Jimmy Buffett is. I let the daughter take a sip of my real margarita. And then afterwards I got a slushie drink outside the restaurant and let her take a sip of that. By the time we got back to the room, everyone was exhausted and we went to bed.
I wouldn't worry about splitting up and letting the kids go on their own. They can do that during the day at the parks. But for the evening, just go to a restaurant together and that will be plenty.