You aren't limited to 3 per day, you are just limited to having only 3 initially at one time. Once you have then used the first 3, you can get additional passes. But you can only then have one additional pass at a time, and you must it before you can get another.
If you want to book all 3 at once, they have to be in the same park. If you wanted to though, you could book 1 pass for a park, use it, and then book a pass for a different park.