Words for someone whose behavior is in question, and the person who is concerned

For our intentional community I am writing up specific processes that can be used when one or more people have problems with another individual's behavior. I'm having trouble coming up with comfortable words to label both the person with concerns and the person the concerns are directed at. It's hard in this kind of community setting because such a word as "complainant" could be taken offense to ... like "it's just saying I'm a complainer." I'm writing up a detailed policy, for which it would be helpful to have single words instead of a phrase each time the person is referred to. This is probably impossible to find the right words, but thought I'd throw it out here anyway.

Example:

The ____________ ["person with the concern"] can request a third party mediation with the ____________ ["person whom they have issues with"].

Solution 1:

"Plaintiff" (in the context of a legal or judicial matter), as the person concerned. "Respondent" as the person whose behaviour is in question.

Plaintiff noun LAW a person who brings a case against another in a court of law. "the plaintiff commenced an action for damages"

Respondent noun 1. LAW a party against whom a petition is filed, especially one in an appeal or a divorce case. 2. a person who replies to something, especially one supplying information for a questionnaire or responding to an advertisement. "out of the many thousands of respondents to our questionnaire, under a fifth were full-time housewives"