Wow.

You should start by reading the stickies for this forum, which will explain about having a notarized letter from both parents indicating their permission for you to travel with the kids. There are a lot of good tips about what to bring and how to bring it -- food, change of clothes, activities, etc.

Book a direct flight, and book a seat for the 20-month old, and bring a car-seat for the plane. I flew EWR-MCO with my older son once when he was around that age, and the 2.5 hour flight felt like it was 2.5 days -- all I can say is good luck to you.