How can I allow multiple registrations in a form?

I'd like to add "add another" at the end of the registration form. If a registrant clicks on "add another ", she can use the following form to register her husband. She can do the same to register her children. The grand payment will be paid by one check or credit card once. 

Also is there a way that the address, phone # can automatically show up after she enters the first few letters or numbers?

Thanks.

How you'd like to add another? Do you want to duplicate the entire form fields or just a section of your form? I understand that you want to calculate the total cost later, but I also need to know if the prices will still be the same. 

You can duplicate the fields (https://www.jotform.com/help/242-How-to-Manage-Multiple-Fields). 

You can show the duplicate fields if the registrant clicks (a radio button or a checkbox field) to register another person (https://www.jotform.com/help/196-Hide-or-Show-Multiple-Fields-at-Once).

You can put the duplicate fields in another page (https://www.jotform.com/help/119-How-to-Create-Multi-Page-Forms). 

You can skip to the last page if the registrant won't click to add a person (https://www.jotform.com/help/350-How-to-skip-pages-using-conditional-logic).

There are ways to accomplish this in the form, but we need to know more about how you'd like it to happen.

As for the second question, I'm sorry but I'm not sure what you mean by that. Do you want to show the fields based on an input? If yes, the show/hide condition will help. I would suggest creating a new thread for this specific question so we can help you with it separately.