There is really only one pool. I mean, they are technically separated, but there are only 2 main seating areas. There is more seating near the main pool vs near the monorail slide pool.
To be very honest, you need to be there by noon if you want a chair. Either get a very early start in the parks, and be back by noon or dedicate one morning to the pool and stay later in the parks (or one evening dedicated to the pool and call it a night early or close down the parks until midnight).
Our family now lets the kids sleep in and we head to the pool after breakfast. Or, we do the pool from like 5-7 and either have dinner poolside or eat a late dinner in the parks around 8 or so.
Chairs are always available after 5pm, and before noon.