Modify Existing Chat Function

We currently utilize two major plugins on our site, Memberpress and UserPro. There is a private messaging platform that we designed and there is the ability for users to share files in those messages to each other. With that being said, there are 2 modifications we need: The first is currently when a user sends a private message to someone, they can only attach one file or picture per message. We need that changed so that you can send multiple images or files at a time. The second is that there is a shared window that displays all images and files someone has shared with a user previously. However, that window only shows for the person that actually shared them and not the person they were shared with. These files need to be visible to both parties.

Please read this carefully before sending any inquiry or questions. We don't want to have to keep explaining what we need done and we need someone that can handle both of these items and not just one.