Hi @michaels,
Thanks for reaching out to auth0 community!
Please check this post Add custom field in Universal Login page. this link will direct you to how you can capture the custom field to your signup page.
or
As per my understanding you can capture the first name, family name through progressive profiling.
Also i checked our product roadmap where adding custom elements to Sign Up page is in our roadmap. hope this helps! Thanks!
Regards,
Pavan.