Check this scenario –
"There's a bug in software your company built."
"Oh, I'm so sorry. You may meet the project in-charge (say he's Jack) for that."
The question now:
What if there are many people in-charge. Say, Jack, Jill, Johny and Michael?
"There's a bug in software your company built."
"Oh, I'm so sorry. You may meet the project in-charges for that." – is certainly incorrect.
If anyone answers that in-charge is always one person, the question's solved!
Note: project in-charge is a noun in this case.
Best Answer
When pluralizing multiple-word terms, we often pluralize the first word, because that is where the noun resides:
However, if the first word (or words) function as a qualifier, we pluralize the noun at the end:
In the case of project in-charge, in-charge is the position title, and project is a qualifier; therefore:
As I mentioned in an earlier comment, even if each project has only one in-charge, that won't negate the need for a plural.