I tried to include as much from the original as I could. While it isn't 1-to-1 (this is a remake, not a port), I'm pretty sure I got most major sequences from the Unity game. That being said, I did also change a lot of things (especially early on). Mostly it's dialogue that's different. The two biggest changes are that 1) Morty uses family names a lot more, in the unity version he almost always calls his mom Beth. Also he never thinks of Morticia as his sister, while its an option to do so in this game. 2) I also tried to have Morty be more into having sex with family, while in the unity version he is always very resistant or degusted by it and it's only because of "points" that he ever does.
Right, I think you're asking how I got the art and animation from the Unity version? I used AssetStuido to unpack all the Texture2D files (then sorted out the new images from the 7000+ files). Animation in the unity game are done via an API called Live2D so they are just texture files on export, not animations. To get the animations, I'm just doing a screen record (windows key + G in windows 10) and looping them as webm files.
The unity game is a bit of a mess from what I can see, most likely why it has so many issues. It's not the worst I've ever seen but it could do with some clean up for sure. That being said, I usually just set it to Texture2D and extract everything, then let the sorting fun for images begin!
This is not a port, it is a remake. The sandbox (which doesn't work that well in the original) has been removed in the renpy version. You can think of this game more like a very fancy image gallery with some viewing options.