Hi,
You can edit the corresponding view file of the listings where you want to add the information via the menu Display>Views in order to add your custom PHP code to run a MySQL query to load the data from the database before displaying it.
I suppose that you actually want to use the first name and last name fields of the default billing address of the customer there.
In that case, you need to run a MySQL query on the hikashop_address table to get the default billing address (address_published = 1 and address_default = 1 and address_type = 'billing').
To know which view file to edit, you can activate the "Display view files" setting of the HikaShop configuration and look again at the page where you want to do your modification. HikaShop will then display which view file displays what part of the page.