I Really Don't Know

A recurring question when people consider the "lore" of the Story of Seasons series (formerly Harvest Moon) is what happens between each game, how do they connect, and are any of the player's possible choices canon? This stuff is usually completely up in the air, and officially games that follow others don't necessarily take place in the same "world" as the previous game to keep player choice open, but that doesn't stop people's minds wandering. Even moreso when a game has a direct sequel, like Harvest Moon to Harvest Moon 64. One of the most endearing elements of 64 is how well it makes the world feel like a lived in place, and that you can tell that the world was going long before you got there and the feeling it will keep going after you leave.

So, since there's a lot to work with to make a theory, let's start exploring it!

Ellen

Starting with the least likely option! Why's Ellen the least likely option? Since she's actually still around in Harvest Moon 64 as Elli's grandmother and, while she mentions your grandfather (the player character from the SNES game), it's very apparent that they were never married. It's honestly kind of surprising considering that she would be one of the first people you befriended after she brings you your pet dog on the first proper day on the farm, but I guess it wasn't love at first sight.

Maria

Maria is a very interesting case. She's one of the characters that isn't really mentioned at all in 64, so we don't really know what happened to her or where she is. The official manga does have her as the primarily love interest, though! Granted, the official manga is also wildly different in presentation and story-telling, almost entirely based on events that don't actually happen in the game, so maybe take that with a grain of salt.

Still, with her being the official love interest for the manga, I think you could pretty reasonably say that that's definitive enough. Though, for me, the biggest wrinkle in this theory is actually from a different sequel to the original story: GBC2. Marie (or Mary) is the only character who appears in both 64 and GBC2's versions of a post-SNES/GB era Flower Bud Village. So, does whatever the protagonist does in the SNES game simply not affect Maria's descendants? Hmm...

Eve

Personally, Eve is one of my picks for "most likely." Have you ever really thought about how the land the protagonist has in the SNES game is enormous, but in 64 it's comparatively small while two more farming operations opened adjacent to it? Also how Eve didn't operate a vineyard in the original game, but, in 64's story, she did? Like, sure, she fermented her own grapes in the original game, but she didn't have a whole big piece of land to work with. I wonder where it came from, y'know?

Even the answer as to why the land would be split is somewhat apparent, thanks to Eve being the only marriage candidate to lose affection every day after being married. What a rough narrative turn...

Nina

Nina is mentioned a few times by Popuri, and the flower shop in 64 is the same one as the SNES game. It's kinda nice to see the place be passed down generation to generation, just like the farm is, but I kinda feel like that's a good reason it probably wasn't Nina. Maybe that time she made Grandpa Pete eat a frog was a turn-off.

Ann

My other "most likely" choice. It's another example where her descendants go from "does not own farm land" to "does" under mysterious circumstances in the 50-year interim between the two games. She's also not really much of a "ranching" type, while only Rick seemed to inherit her distinctive traits of inventing and tinkering.

With the player being able to have at least three kids in the SNES game, that could be a looot of land for the descendants to split up, and we already know that your dad in 64 didn't take any. I guess it's kinda notable that Green Ranch is directly south of your farm, and not across the way like the vineyard is. Hrm...

None of the Above