There is only a video object, I modify the path of the video using the metadata of cloud reco, but it looks like it creates more videos on runtime or something like that, I don't really get it.

You might want to programmatically turn on/off the the multiple video objects as needed based on recognizing different targets. You can also experiment with different scales for the videos and see what that does for the size.

You may also want to work through this FAQ:

https://developer.vuforia.com/forum/faq/unity-how-do-i-create-simple-videoplayback-app

Its an android device. When I unload the video and load a new one, if the first video was paused then it shows the "busy texture" over the first video paused (as if it was a background) when loading the second video.

I also, have those two bugs regarding the video width & height being half of the normal size (which is fixed by going into full screen mode and going back) and two videos playing on the same prefab. I attached a screenshot of the problems that I'm having, please help.

Are you testing the video playback within Unity or on a device?

My main problem is that when I change from a target A to a target B the video played on target A is gonna get paused, and when I scan the target B, since the video file isn't local it is gonna show the "busy icon" over the paused video (from target A), and I don't want this to happen, that's why I'd like to clear completely the object before loading a new video.

Also, sometimes, the video is displayed on half of the target size, It plays correctly but the size isn't the one that I specified. If I go to full screen and then back, it shows the video on the rigth size, its a weird bug.

Can I give you my project so you can test it?

If you are using the VideoPlayback sample app in Unity, then refer to the Play(), Pause(), and SeekTo() methods of the VideoPlayerHelper class.