Automate Audio File Uploads to WP Webpage

Currently a VA (Virtual assistant) goes to a 3rd party website and selects a .wav audio file and uploads the audio file to their computer and then converts it to an .mp3 file. Then the VA uploads the .mp3 file to my WP website’s media library. Then the VA puts the .mp3 into an audio player on a page on the website. This assignment is to automate this process so the VA can use a form you create to upload the audio files from the 3rd party site and with something like a WP short code to display the audio in an audio player on various pages on my website. I need this accomplished in a way that the VA would not need admin access to the WP website. Currently we convert the .wav file to an .mp3 file before we post it in the audio player on the website. I would need that step either automated or eliminated. I currently host my video files in amazon s3 and would like your suggestion if I should host my audio files there or on my website. I would also need your help in selecting an audio player. The VA currently selects 12 audios or more each week and uploads each to a different page on the website for one company. Eventually that task will be done for multiple companies and multiple pages for each company so this system needs to be compatible for that. The upload form would need a dropdown of companies for the VA to select from, then a second dropdown to select which page of the selected company to display the audio on.