Try starting
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Click on the version of VH you're looking to download, then click the blue 'Code' button on the top right and choose to download as a ZIP file from the drop-down menu that should appear afterward. That should let you download the latest Github version. If you're asked for a password when trying to unzip, I believe it's the name of the main heroine from each version - Nanako for most, Serena for Katteban. (At least, that was the case the last time I downloaded VH myself, which was a very long time ago.)
To my understanding the main differences are:
1) VH01 - The original, made on RPG Maker 2000 starting in 2007 IIRC. Should be the most complete, but also the clunkiest of all the versions of VH. Both Nanako and Serena are playable with plenty of content (but also bugs) to navigate, Nanako had the most overall but Serena had a decent amount in as well. To my understanding most if not all of the original devs left a very long time ago, and there's been virtually no new content made for it in years (only translations of existing content at best) since nobody really wants to work with RPGM2K if they don't absolutely have to these days - the last big content drop for VH01 I can recall was the inclusion of Eisen & a rather buggy jungle storyline, and that was about a decade ago.
2) VH Katteban - A Serena-centric fork made by her creator (Waru, the same guy who made VP) after falling out with the VH team over creative differences in the early 2010s. More content for Serena naturally, existing content from base VH was reworked to be rather more rapey (as you might guess Waru was really into the 'Violated' part of Violated Heroine/Princess), and she was given a facelift to seem even more childlike (I would say VP-Serena's design occupies a midpoint between base VH-Serena and the downright kindergartner-y look of VHK-Serena, but is closer to the former). Has been abandoned for years since Waru went all-in on making VP instead.
3) VHMV - The most modern version, made on RPG Maker MV in more recent years. As you have observed, it's the version being updated most regularly nowadays. The last time I downloaded VHMV, they were still porting content over and only Nanako was playable, unsure if that has changed significantly as it's been a while since.
Missing from that repository is
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a fork of VHK made after Waru stopped updating it, which is basically a Serena-only scene viewer with little gameplay and which never got even a partial translation as VHK did to my knowledge. Said it before but I'm not sure if that will ever be updated again, Rosemary had been working on a promising confinement storyline (you can see some completed assets posted to his VHR-specific blog entry on the same website) shortly before pivoting to making his VP 'different Serena personalities' mod and I'm guessing that's taking all his modding time & energy atm (especially as he's started working on it again after taking a break following the Christmas 1.01 release).
