well not so easy to answer.
1. they are in the princess pavillon.
2. when you are in line, they ask you if you are here the first time. When not you tell them wich princess yo already saw. And they make sure, you won`t see the same one. (I think, they learnt from complaints).
3. the princessess switch every 30-45 Min. (that`s what they told us 2 weeks ago).
4. they explained us, there can be 4 or more princesses a day! So even if they tell you Arielle and Belle are there, it can be at the time you get there, someone else is there.
5. I think Arielle is easier to be seen then Belle (I love Belle).
6. try your irish charm anyway!
Have a great trip