Take input video and personalized content, and replace sections of the input video with AI generated personalized content, and restitch the video

We are trying to create an app similar to [login to view URL], where the user can provide an input video, maybe they are saying something like "Hi David, I wanted to say hello and welcome to the company!" or something like that, the video can be any length. Then, the user should be able to provide the section they want to customize, something like "Hi @firstname, I wanted to say hello and welcome to the company!" Then, for a list of, say, 5 names, e.g. Alice, Bob, Candice, David, Earl, we want to "generate" another version of the input video using AI (deepfake audio and video) of the person in the video believably saying "Alice", then, we want to remove "David" from the original source video, and replace it with our deepfaked clip of the user saying "Alice", and make the final product feel seamless to the end user. If you take a look at [login to view URL], you can understand clearly what I mean.