I have a few questions:
1: Does this work with Visustellas ATB system?
2: If I were to do <Dual:1,Slash,2,Ice>; <Dual:1,Slash,3,Ice>
That skill will activate if player 1 uses Slash and if Player 2 or Player 3 uses Ice?
Let your actors combine their skills in RPG Maker MV and MZ · By
1. Basic functionality should be battle-system-agnostic, and I can make an update if it doesn't work (provided I have access to the plugin, at least). However, turn linking (IOWs, having a dualtech consume the turn of all involved actors) is a more complicated matter. I don't know how Visustella's ATB differs from the built-in ATB, but if it is significantly different, then turn linking may not work; heck, for the built-in ATB, it only currently works with one setting. (I have not used Visustella's plugins outside some testing scenarios; my own main game project is MV, not MZ.)
2. No.
2a. A dualtech is its own skill that has to be used manually. Have you played Chrono Trigger? The functionality of dualtechs via this plugin is similar to how it works in Chrono Trigger. In the case of the first tag, it will require actor 1 to be able to use Slash and actor 2 to be able to use Ice, and the component skills determine skill cost handling, but you use the dualtech by directly using the dualtech.
2b. Do not assign the "Dual" tag to the same skill twice. You might be better off creating two copies of the dualtech instead - one copy for actors 1 and 2, and another for actors 1 and 3.