You could set up a Profile as you can specify where people go when they submit it.
therefore you should be able to set Profile A to redirect to Profile B on submission.
I expect this will work 'as is' for logged in users.
There would be a problem if you send someone to Profile A via a link with a checksum as the checksum will 'expire' before they get to ...
For others having this same problem, please note that you have to also make sure that in the section "Who can register accounts?" in /admin/config/people/settings ("Configuration" > "User accounts" > "Account settings" in the backdrop menu) that you allow for "Visitors" or "Visitors, but ...
I don't use Joomla but it should be the same as Drupal / WordPress where you need to enable the permission "CiviCRM: access all custom data" for anonymous user.
Otherwise, you need to define an ACL to explicitly add the permission for everyone to the custom group containing the custom field. I feel that it's more complex and rarely needed but it ...
So I just went through and created a custom profile. I added three fields drawn from individual:
I entered a sample with a local business and the resulting contact had the appropriate relationship.
Is this what you were trying to accomplish?