This is a relatively common question from EVE players -- "I have 2 miners and a hauler" etc.
What you're looking for is
Repeater Target Action. This can go in a
Mapped Key that turns on your
Mouse broadcasting (via a
Repeater State Action, as configured under "Always On"
Key Map from the
Quick Setup Wizard).
What you're describing is accomplished with 2 Repeater Target Actions. One of them has a
Target of Window 2 (for when broadcasting
from window 2), with the "New Repeater Target" field set to window 3. The other is vice versa -- Target=3, New Repeater Target=2.
So to set this up, you can:
1. In the top pane, under Key Maps, select "Always On"
2. In the bottom left pane, under Mapped Keys, expand "Activate Repeat" so that under it you see Steps, 1 and 2.
3. Select the 1 under its Steps so that to the right you see Step, Actions, and it has a few actions in it that turn on repeating and adjust the Toggles
Click Bar4. In the bottom right pane, right click "Actions" and under Repeater Actions, select Repeater Target Action
5. Set the Target to window 2 (slot 2)
6. Set the New Repeater Target to window 3 (slot 3)
7. Repeat steps 4 through 6, except with the opposite Target and New Repeater Targets
8. Export to Inner Space and try it out