Summary from comments included.
All are correct.
The examples you cite illustrate the ambiguity of the rules of English grammatical construction in certain edge cases.
The central issue of your question is whether modifying clauses should be singular or plural when the object of the clause is singular (by inference) but the object which the clause modifies is plural. In other words, when deciding modifier plurality, which object controls?
The discussion in the comments suggests no hard and fast rule exists. I agree.
What the writer or speaker chooses will be a matter of subjective preference coupled with contextual reasoning. In your examples, I think all are correct. Or, perhaps more accurately, none can be proven incorrect.