There's a wiki article on this too - List of characters played by multiple actors in the same film
The highest film I can find that definitely meets the requirement is:
Palindromes - eight actors playing one role:
All of the below actors play Aviva
Emani Sledge, Valerie Shusterov, Hannah Freiman, Rachel Corr, Will
Denton, Sharon Wilkins, Shayna Levine and Jennifer Jason Leigh as
Aviva in Palindromes (2004)
However, if we accept a slightly more unusual film:
Audition - 50 actors playing one role, 50 actresses playing the other role
This may seem like a bit of a cheat, but as you asked for movie characters, the following all play Man:
Nicholas Baroudi, Bryant Boon, Grant Boyd, Tyler Burke, Sean Buttimer,
Nicholas E. Calhoun, Andrew Casanova, Steve Cavanaugh, Donovan
Christie Jr., Paul Corning Jr., Adrian Corrie, Dan Cozzens, Thompson
B. Crozier, Dan de Jesus, Marc T. Engberg, Jonathan Iglesias, George
Iliopoulos, Benjamin Jones, Adrian Kelly, Brandon Kieffer, Aidan
Kinney, Jonathan Laffey, Christopher La Forgia, Fernando L. Lamberty,
Dylan Landon, Mike Lubik, Shaka Malik, Christian Manzo, Robert
Maxwell, Benedict Mazurek, Adam Miller, Seth Andrew Miller, Austin
Mitchell, Zachary Mooren, David Andrew Morton, Kevin Needham, Eric
James O'Keefe, Philip Oros, Gabriel Pardo, Christopher Patten, Ernest
G. Perry, Jeff Ronan, Andrew Saunders, David Seamon, Gianmarco Soresi,
Yaron Urbas, Nicholas Urda, Chris Viemeister, Bryan Williams, and
Peter Zerneck as Man in Audition (2015)
And the following all play Woman:
Szalene Anthony, Milee Bang, Christina Barrell, Caroline Bloom, Jess
Brown, Julia Burnside, Erica Camarano, Blaire Carson, Senta Cassell,
Teegan Curitz, Mary Davila-Delgado, Leah Dowdy, Emily Fleischer,
Lolita Foster, Chelsea Frei, Kate Gunther, Casey Ann Hayward, Sarah
Himadeh, Corinne Hundt, Javelyn, Emilyn Kowaleski, Erica LaTorra,
Jeanne Lau, Marion Le Coguic, Mary Linehan, Cara Loften, Maribel
Martinez, Ariella Mastroianni, Maggie McGuire, Velta Moore, Hadas
Nuriel, Angel Pai, Cassandra Paras, Andi Potamkin, Sam Quartin,
Jacqueline Real, Katelyn Sarazen, Sarah Schoofs, Alex Megan Schell,
Nadia Serantes, Robin Singer, Paige Spara, Katie Rose Summerfield,
Khloe Sunga, Rebecca Sussman, Amanda Tudor, Juliette Verroye, Jenna
Williams, Margaret Keane Williams, and Francesca C. Zucchetti as Woman
in Audition (2015)
To quote from the IMDB article on Audition:
A romance is portrayed by one hundred actors who audition for the two
lead roles and the chance to perform the final terrifying act.
What is love? New York filmmaker Matt Herron spent over 15 years
peeling back layers of expectations and disappointments to explore the
mysteries of this complex emotion through his powerful new film,
AUDITION. Set in the midst of a real-life acting competition, this
cautionary narrative within a documentary is a sensually-riveting
journey every adult should see.
So technically all of these people are playing the same role - that of the "man" or that of the "woman". If you check the film's credits, they are all credited as so, and as the OP asked Which movie-character was played by the most amount of distinct actors in a single movie?, this does meet the requirements.