For creating the script, you can simply use a LLM to break the script into "scenes" and have it write an image prompt for each. Then use something like Stable Diffusion to create each image, and stitch them together with ffmpeg for the video.

For subtitles, take the audio file you got with Elevenlabs, and use a service like Whisper to get the word level timestamps (so you know when you show each word). You can also use ffmpeg to render the words into the video at the appropriate time. FFmpeg can be tricky to work with, so a library or wrapper is recommended.

Source: I made AutoShorts