Kinda silly CC characters question.

[Duke Serkol]

As many other RPG players, I'm a packrat. I always try my darnedest to get everything I can in RPG games.
This extends also to characters and when playing CC I regularly strived to get as many as possible.

But now I've been wondering... what characters are absolutely necessary to get, even temporarily, in your party in order to play all the way to the Dragon God?

I don't believe any minimalist guide to this game exists, so I'm going to go and guess, but I think it's actually very few.

Serge   for obvious reasons.
Kid, I'm assuming you can't proceed without her.
Guile or Nikki or Pierre. You must have one of these to get into Viper Manor, right?   
Lynx again for obvious reasons.
Harle joins automatically, right? (Does Sprigg too?)
Norris? (Is he necessary to get in the Manor ruins?)
Karsh, Zoah, Marcy and Viper   might join automatically after Chronopolis?
Starky you need to get to Terra Tower.

And I think that's it? Are there any others that necessarily join you on your way to fighting the Dragon God?
Can you skip/refuse any of the above from joining your group without being stuck?

[Acacia Sgt]

It's somewhat hard to define a minimalist point here. Considering many of the ones that join automatically aren't really necessary to progress the game. And not all can be turned down when they wish to join.

By the way, despite her importance, Kid actually is never forced to join the party. You can play the whole game without ever getting her to join. It's really up to player choice if she is in or not. This applies to the many other opportunities on the game. You can either refuse, or just don't do it at all.

[Mr Bekkler]

It would be kind of nice to get a list of absolutely necessary (meaning the game won't go on without them) characters. Include characters that the game won't let you refuse and see how short the list is, then compare it to Chrono Trigger's playable characters incessantly in my head.

Anybody who memorized the hell out of cross who knows off the top of their head?

[alfadorredux]

Arguably, in addition to the Viper Manor guides, Macha/Korcha (for one boat), Norris (for the other boat), Starky (for the flying boat), and Steena (for the Chrono Cross) are all necessary to the game's progress.

I think Fargo, Grobyc, Harle, Karsh, Leah, Marcy, Orcha, Radius, Riddel, Sneff, Viper, and ZOAH also auto-join (I can't absolutely guarantee that none of them can be refused, though). Everyone else should be refusable/missable.

[Kodokami]

From the looks of this site, these may be the only characters required to join:

Guile/Nikki/Pierre
Korcha & Razzly (save Kid route)
Lynx
Sprigg
Harle
Radius
Norris
Karsh
Zoah
Orcha
Grobyc
Viper
Fargo
Marcy
Leah
Starky
Steena

I'm not sure how accurate this is though. For instance, I don't remember the fight against MegaStarky being required (though I don't know how you would reach Terra Tower without him). And for some reason I can't get Kid to NOT join my party. I must be doing something wrong.

[alfadorredux]

Razzly can be bypassed--it's possible to pass through the Pentapus' lair without speaking to her. (Been there, done that.) Sprigg, however, should have been on my list--don't know how I missed her.

[Duke Serkol]

Well, would you look at that... I thought I might end up being called a noob for not knowing this, but it turns out I stumbled onto a very obscure bit of trivia here with my question.

It would be kind of nice to get a list of absolutely necessary (meaning the game won't go on without them) characters. Include characters that the game won't let you refuse

Yes, that's exactly what I'd like to know.

Macha/Korcha (for one boat)
...
and Steena (for the Chrono Cross)

Oh, you have to let those join? I thought you could turn down their requests (with Macha/Korcha only acting as ferry then, or letting you borrow the boat)

I think Fargo, Grobyc, Harle, Karsh, Leah, Marcy, Orcha, Radius, Riddel, Sneff, Viper, and ZOAH also auto-join (I can't absolutely guarantee that none of them can be refused, though).

I think Grobyc and Riddel can be refused, maybe Radius and Leah too. I'm pretty sure you can miss Orcha and Sneff entirely.

But my memory's rather fuzzy so...

[alfadorredux]

Oh, you have to let those join? I thought you could turn down their requests (with Macha/Korcha only acting as ferry then, or letting you borrow the boat)

...

I think Grobyc and Riddel can be refused, maybe Radius and Leah too. I'm pretty sure you can miss Orcha and Sneff entirely.

But my memory's rather fuzzy so...

I can't remember who you can or can't refuse either, since I've never seen the point of refusing (except for Kid's initial request, since her presence in the party blocks Leena from joining)--it probably would have been more accurate for me to say that those are the characters who aren't missable. Orcha can't be missed, because the Hell's Cook fight is a required part of the rescue-Riddel plot sequence. Likewise, you can't miss Sneff, because the turned-into-cats sequence is required if you ever want to get off the Zelbess. However, it's likely that they're both refusable.

[Duke Serkol]

But don't you recruit Orcha and Sneff by going to see them after their mandatory part in the story is over? That's the way I remember it. I very nearly certain that was the case with Sneff.

[alfadorredux]

It's possible. (Having made them unrecruitable in Chrono Helix means that I don't really remember how you got them in the real game...)

[utunnels]

Sneff - yes
Orcha - no, he joined automatically