How can I have an event trigger that allows on touch, even if theres another finger somewhere else on the screen?
Just have 2 images or whatever with the event trigger and everything should work fine when you run the game on a mobile device. Windows only supports one pointer, so you will have to test your game on a physical device.
If you are talking about Event System component, it already supports multi-touch as far as i know.
If you are talking about writing you own script, then you can just use a foreach loop to get all the touches and use them whereever you want.