Someone who's played both the remakes and the originals more intensely is going to have to correct me if I'm wrong but the remakes don't radically change a lot? I always went by the image on the
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. When and where the remakes contradict the originals, the remake is canon over it, but the places where it actually does that are few and far in between.
01 and 02 Kai definitely follow the same plot but they differently characterize a few of the characters in a way that's never really mentioned again and probably works worse with canon than the actual older games. 01 also tries to "animeify" the game more by giving kanami and especially maris weird 2nd phase boss fights and maris just kind of like.. explodes and goes crazy?
In 01 the remake exclusive characterization of Rance is about how insecure he is of being seen as a "country bumpkin" and that term is probably said more in this game than every other rance game combined. 02 makes Rance a less serious character than the Original and gets rid of A LOT of CGs the original had in favor of little chibi mini CGs or none at all. An example of the less serious Rance would be during the confrontation with Mill he ends up putting a sword to Milli's throat in order to get Mill to stop producing phantoms, in the original he holds his ground, even brings the blade closer, and doesn't do anything that would indicate that he wouldn't actually do it (though yeah, he actually wouldn't.) and in the remake he puts the blade to Milli and goes on a rant about how he's not actually going to do it and gets into a mild screaming match with Maria about how he was never actually planning on killing Milli (while still holding the blade to her) and Mill just surrenders anyways.
You can definitely tell that they wrote 02 Kai coming off of Sengoku because they gave Bird an obsession with sweet potatoes that is never really referred to again, especially not to the amount he has one in 02. Sengoku started some weird little meme about how all the characters loved eating sweet potatoes, especially Ryouma and her group, and they wrote Bird to take advantage of that meme regardless of how it actually affects his character. Every single person he meets he offers them a Sweet potato, he carries like 20 around in his pockets and he's constantly munching on them.
The entire Menad quest in Rance 01 is also remake exclusive content, there was a graveyard quest in a specific version of Rance 1 but I'm pretty sure it was for the girl who levels you up instead of the gatekeeper. I also know that Rance 03 does A LOT of things differently than 3 but not very many specifics.