Yes, you can mass delete the User-defined fields (UDF) for ALL Families at once from the All Families menu > Clear UDF Answers.
Additionally, you can delete all answers in User-defined fields from the All Families menu. Go to Families (menu) > All Families and select the families in the 1st column with a checkbox. Click the More (Mass Actions) button and select Clear UDF Answers.
The User ID must have this permission under Families to process a mass delete:
- Clear Family User Defined Fields and Family/Student Fixed Fees and Discounts