This type of logic can be most easily implemented with checkboxes. If you have a field that should only be filled out after two other fields meet certain conditions, then ideally you would only have that field appear when those conditions have been met. However, DocuSign only allows one trigger to affect dependent fields at a time, so you cannot simply have two checkboxes trigger the same field. Instead, you must create two invisible trigger fields with preset values and then use a formula to combine those values. This formula field can then be used as the trigger for the required field you want to appear.
First, add two small text fields next to your checkboxes and add a ‘1’ to each, formatting the text to be white and switching the fields to ‘Read Only’ to make them invisible. Then, create a conditional rule for each checkbox that will make one of the invisible fields appear when the box is checked. Next, add a formula field and set it to equal [A] + [B] (A and B being the data labels for the two invisible fields valued at 1). Now you can set this formula field as the trigger for the required field you want the signer to see, having it appear when the formula equals 2.
*arrows represent conditional rule, pointing from trigger to field to appear