Can you pause a video in a marker with trigger?

I understand you have two markers, each holding a video. Nathanial has set up a perfect example of how it's done with JavaScript, and I don't think there is any other way to execute what you asked for. Alternatively, since you have two videos, you can Execute JavaScript when the timeline starts on this slide:

let videos = document.querySelectorAll('[data-video-id*="video"]');
window.video0 = videos[0];
window.video1 = videos[1];

window.video0.onplaying = function() {
    setVar('videoPlayed', '0')
}

window.video1.onplaying = function() {
    setVar('videoPlayed', '1')
}

Then Execute JavaScript when the user presses something (ex. space)

 if (getVar('videoPlayed') === 0) {
    if (!video0.paused) {
    video0.pause();
    video1.pause();
   } else {
     video0.play();
   }
} 

if (getVar('videoPlayed') === 1) {
    if (!video1.paused) {
    video1.pause();
    video0.pause();
   } else {
     video1.play();
   }
}

Assuming you have a number variable named 'videoPlayed' created in Storyline. This way, each video can be paused and played without interfering with each other. Please refer to the attached Storyline file for reference.