Remember, you are responsible for the tone, atmosphere and working environment. Even if you do not take any immediate action on a particular complaint, you probably should consult with your lawyer, and document, document, document. May be a time to address boundaries with your workers if that is the case.
Most employees have anziety about being evaluated, especially with forms.
You can not evaluate someone on something that is outside their duties. Create individualized performance goals. Use narratives instead of ranking scales. Remember that evaluations are a paper trail. Do them often.