Mary,
That sounds great, perhaps we can get together over the weekend, if your kids can spare you from visiting. If you want to check out some of the other Springs around the area Michael is a great guide as well as assist you with your buoyancy. That can be a bit tricky and is one of the best skills in diving to fine tune as it is a great benefit in the long run.
So, on the manatee thing, if booking with a boat, perhaps they have other divers that you guys could dive with? Or does one of you need to be with the grandkids? From the boats, they only allow diving in Kings Spring in Crystal River. The viz can be a bit cloudy, so not the crystal clear water you see in most Springs...however the Manatees do venture in there and there is a cool statue to see. Three Sisters Spring is closed to diving right now, but the water is beautiful.
Look forward to meeting you and diving with you both. You can’t come to Florida and not dive and dive together :)