0. For learning about the Pro system I would suggest
MiRai's video series. The Pro system is as much a philosophy of how you structure your ISBoxer profile as anything. That hasn't changed since those videos were made. If there are specific differences in ISB42, then they can be addressed as they arise. That is the best, most recent resource I know of.
1. You need to add a Send Next Click Action to Step 1 (the only Step) of the Ground AOE Mapped Key in the ISB42 - Combat Hotkeys. I have mine set up to "Block click from current window" and then you can set the Target to "Window:All w/ Current". If you want to round-robin the Ground AOE, you will need to set the round-robin option for both actions, the existing one and the one you added. If not all of your characters have Ground AOE abilities, you may want to use an Action Target Group as the Target of those Actions.
If any of the above terms are unfamiliar to you, there are descriptions in the
ISBoxer wiki.
2. MiRai talks about the concepts involved in setting up DPS rotations in the Pro system videos linked above. This is not easy. Even with something as easy to play as BM Hunters, my secondary characters only do about 80% of the damage of my main. The more other resources, cooldowns, procs that you have to manage, the worse this percentage is going to get. For discussion of multiboxing rotations, class compositions and other aspects of multiboxing not specifically related to ISBoxer, you may find better resources at
dual-boxing.com.