I guess it would help if you had more specific questions about what you want to change?
For the pool walls though-- When a pool is built so that you can see the lower level walls, like this was, they're just walls. Which means you can put windows in them! That's how it was done there. Unfortunately, when you're viewing that lower level looking into those windows, you don't see the sims swimming in it. It seems to be, because those sims are actually on the floor above.