Prevent users from entering honorifics (Mr. / Mrs. / Ms.) in the First Name field

We have a high-throughput User Info intake form that get thousands of submissions everyday. The form, among other fields, has fields for First Name and Last Name. The form text is translated to the regions where we are getting the users from. However we still see folks entering Mr. Ms. Mrs Dr. etc instead of the First Name. And Full Name in the Last Name field.

We are adding field validation to prevent users from entering these honorifics in the Firstname field.

However I am wondering if there are other things that we can do to make it more clear to the end-users that they are supposed to enter their First Name and not honorifics.

p.s. We don't want to add a Title field, like some other sites do.