Might want to give some more thought to the swimming. Its going to be hard for you to police two little ones in the pool. You might want to buy a swim vest
like this. That will give the kids some more freedom to jump around without you trying to have 20 foot arms.
Start looking at the heights. 40" for Splash Mountain, Thunder Mountain, etc. I think Disney has a good webpage for telling you the height restrictions per ride. You may want start planning out what rides you can hit and which ones you have to avoid because of height or you can't get all three of you on.
Because of the potential ride problems, you might want to focus on shows and parades. That way everyone can enjoy the fun.
I think Animal Kingdom should be a must, maybe a character breakfast at the Tusker House. There are some good shows there that would work well with a single parent trying to keep two kids engaged (Nemo, Lion King, etc)
Spend some time at
Disney Moms forum and search for single parent. You'll find lots of good advice.
Hollywood Studios should be an option for Disney Playhouse Live and Little Mermaid shows (assuming it has reopened by then).
You might want to consider a side trip to Seaworld. Lots of shows for the kids to get into. They can feed and touch dolphins and little stingrays. The dolphin show there is great as well as the whale show. There is an otter and seal show that is good too.
IMHO, focusing on the shows will be the best way have fun as a group without you pulling your hair out.
I think those are great ages by the way! Just took my 3 and 5 year old for their second trip. Perfect ages to enjoy the characters!