The girls would remain on the boat (with very little boating experience between them since it has nothing to do with shopping or mani/pedi days) and I'm guessing we'd be moored by a wreck and maybe drifting while at the reef.
This would be my biggest concern. You should have someone with experience on the boat. Current can be strong, and you could find yourself too far away from the boat.
A charter would probably be easier, and maybe cheaper as well, but I can understand the desire to do it on your own.
I go down to the Keys with my own boat each summer. We stay a few islands up from KW. If you know what you are doing with a boat, you can make it work. Being familiar with reading a chartplotter and bottom machine will help. It’s not too hard to find the reef if you know what you are looking for.
Getting there can be a challenge, though. The channels in the Keys can be unique. Where we usually stay, the resort has a channel around the resort, and the canals are deep enough. To get to the ICW, there is a small marked box. Literally just enough room for my boat, and not much else. From there, it’s a long run over the deeper parts of the flat to get to the actual channel. The idea is to line up in the box and pop up on plane quick. That gets the boat out of the water. Procedure is reversed on the way in. I always see those that don’t know the technique, and their props are cutting a path though the mud and grass. Don’t do that.
Boat rental places will probably have some spots marked in the boat, but usually just public numbers. Quality of the rental outfit can vary greatly.
Like I said, my biggest concern is not having experienced boaters on the boat while diving.
I should add, it’s very easy to get in trouble on the water in the Keys. The shallow areas aren’t just soft mud. Large rocky areas and coral heads are common. The first few years I went down, I followed a friend that practically grew up down there. That cut the learning curve way down.
Diving in the Keys is very different from freshwater diving, and boating in the Keys is not all that similar to lake boating.