php - access folder on another site on the same server

php - access folder on another site on the same server

I have a dedicated server running centos, I have serval sites on this
server and all of them are mine. I want use php to upload files -videos-
where the file exit on the other site.
let me explain /home/user1/public_html/uploads => the videos are here =>
domain.com
/home/user2/public_html/upload.php => the php file to upload on another
site on the same server => domain.net
how can I let the other site upload a video from my other website that on
the same server.
I wish that was clear