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 <PERSON>
<PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON> and <PERSON> as <PERSON> 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:
<PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, and <PERSON> as Man in Audition (2015)
And the following all play Woman:
<PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON>, and <PERSON> 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 <PERSON> 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. 569