Re: Plural Objects
You can use any combination as long as the meaning is clear. People wear only one uniform at a time, and no one uniform is shared by two people at a time, so either sentence is clear.
If you are installing something that requires two holes at each location, then "holes" would be the obvious choice. But if you are just drilling one hole per location, then mark the locations where each hole will be drilled is quite clear. (Note I said "each hole" the "the hole" for added clarity.
When there could be confusion as to whether each person had one or more than one, then rewriting is needed.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.