If you want to use the original voices from a movie or TV show in your animation but can’t afford to hire the original actors, here's an example of how to do it.
First, it is legal as long as it is a parody and you don't intend to sell the animation.
If you don't have a photographic memory and know exactly who said what and when in each episode, you'll need transcripts of each episode. You can find them online, mostly on fan sites like Fandom.com. Download each transcript as a text or PDF file. I recommend using the Firefox browser with the “Print to PDF” add-on. This add-on can download text only, without backgrounds.
Then, you will need a tool like Clapgrep to search the text files for what you are looking for.
Next, you need to have all the episodes of the series or movie from which you want the original voice. Nearly all series are available online, such as on wcoflix.tv.
Once you've located the text in the video, use a tool like Ocenaudio to record the spoken line. If there is background noise, music, or a hall effect, you can remove it using AI. The service is free if the uploaded sound file is shorter than 10 seconds. The sound file will be divided into speech and music/noise. Then, you can record the result again with only the voice. However, this AI is still in its beginning stages, so some background noise may be too loud and make the original voice sound awkward. The quality of the result depends on the quality of the original sound. If possible, you should take another sample.
Another option is to use AI to create a voice that sounds similar to the original. Currently, I don't know of a single site that can create a perfect voice; most of those services are not free. The ones I know of still can't change the mood of the voice, like whispering, shouting in fear, sounding curious or seductive, and so on. In a few years, this will surely have changed with updates. It won't be long before you can create your own episode of your favorite series using AI, if you can afford it.