This requires the same skills as your question about selecting random items from a list. I'm sure there are many ways to do this, but here's one suggestion:
Setup:
1) Create a list
2) Add each of the letter actors to the list
To shuffle:
[Repeat] loop for number of items in the list
Select random item (actor) from list
Move actor to first position
Delete the actor from the list, so it can't be chosen again
[end of loop]
Tip:
To place the actors, inside the loop, move each actor to (e.g.) X = 100 + (item number * 40). Make the Y a fixed number such as 300.
This will move the first actor to 100, 300 the second actor to 140, 300, the third to 180, 300 - etc.
Before you start, break the problem down into steps. For example. Work out how to add actors to a list. Then work out how to create a repeat that will loop for each item in the list.